Here's my system log spanning the time when the bug occurred.  The log starts around the time when I used System Updater while playing chess, and ends at the place where I rebooted.   I don't understand why there were so many thread creations owned by 1000 ... is that the symptom of this bug? 

May 13 08:11:25 arpeggio AptDaemon: INFO: CommitPackages() was called: dbus.Array([dbus.String('')], signature=dbus.Signature('s')), dbus.Array([dbus.String('')], signature=dbus.Signature('s')), dbus.Array([dbus.String('')], signature=dbus.Signature('s')), dbus.Array([dbus.String('')], signature=dbus.Signature('s')), dbus.Array([dbus.String('account-plugin-aim'), dbus.String('account-plugin-jabber'), dbus.String('account-plugin-salut'), dbus.String('account-plugin-yahoo'), dbus.String('empathy'), dbus.String('empathy-common'), dbus.String('libfreetype6'), dbus.String('libfreetype6:i386'), dbus.String('liblightdm-gobject-1-0'), dbus.String('libnautilus-extension1a'), dbus.String('lightdm'), dbus.String('linux-firmware'), dbus.String('mcp-account-manager-uoa'), dbus.String('nautilus-data'), dbus.String('nautilus-sendto-empathy'), dbus.String('patch')], signature=dbus.Signature('s')), dbus.Array([dbus.String('')], signature=dbus.Signature('s'))
May 13 08:11:25 arpeggio AptDaemon.Trans: INFO: Queuing transaction /org/debian/apt/transaction/f2d1b68012b5467ca9225b3252b23996
May 13 08:11:25 arpeggio AptDaemon.Worker: INFO: Simulating trans: /org/debian/apt/transaction/f2d1b68012b5467ca9225b3252b23996
May 13 08:11:25 arpeggio AptDaemon.Worker: INFO: Committing packages: dbus.Array([], signature=dbus.Signature('s')), dbus.Array([], signature=dbus.Signature('s')), dbus.Array([], signature=dbus.Signature('s')), dbus.Array([], signature=dbus.Signature('s')), dbus.Array([dbus.String('account-plugin-aim'), dbus.String('account-plugin-jabber'), dbus.String('account-plugin-salut'), dbus.String('account-plugin-yahoo'), dbus.String('empathy'), dbus.String('empathy-common'), dbus.String('libfreetype6'), dbus.String('libfreetype6:i386'), dbus.String('liblightdm-gobject-1-0'), dbus.String('libnautilus-extension1a'), dbus.String('lightdm'), dbus.String('linux-firmware'), dbus.String('mcp-account-manager-uoa'), dbus.String('nautilus-data'), dbus.String('nautilus-sendto-empathy'), dbus.String('patch')], signature=dbus.Signature('s')), dbus.Array([], signature=dbus.Signature('s'))
May 13 08:11:25 arpeggio AptDaemon.Worker: INFO: Processing transaction /org/debian/apt/transaction/f2d1b68012b5467ca9225b3252b23996
May 13 08:12:17 arpeggio rtkit-daemon[1493]: Successfully made thread 5343 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:12:17 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:12:52 arpeggio dbus[483]: [system] Reloaded configuration
May 13 08:12:54 arpeggio NetworkManager[992]: <info> kernel firmware directory '/lib/firmware' changed
May 13 08:12:58 arpeggio AptDaemon.Worker: INFO: Finished transaction /org/debian/apt/transaction/f2d1b68012b5467ca9225b3252b23996
May 13 08:14:15 arpeggio rtkit-daemon[1493]: Successfully made thread 6171 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:14:15 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:14:22 arpeggio rtkit-daemon[1493]: Successfully made thread 6186 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:14:22 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:14:27 arpeggio rtkit-daemon[1493]: Successfully made thread 6195 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:14:27 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:14:31 arpeggio rtkit-daemon[1493]: Successfully made thread 6197 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:14:31 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:14:35 arpeggio rtkit-daemon[1493]: Successfully made thread 6199 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:14:35 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:14:41 arpeggio rtkit-daemon[1493]: Successfully made thread 6201 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:14:41 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:14:47 arpeggio rtkit-daemon[1493]: Successfully made thread 6203 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:14:47 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:15:18 arpeggio rtkit-daemon[1493]: Successfully made thread 6205 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:15:18 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:15:24 arpeggio rtkit-daemon[1493]: Successfully made thread 6208 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:15:24 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:15:39 arpeggio rtkit-daemon[1493]: Successfully made thread 6216 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:15:39 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:15:44 arpeggio rtkit-daemon[1493]: Successfully made thread 6220 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:15:44 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:16:09 arpeggio rtkit-daemon[1493]: Successfully made thread 6222 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:16:09 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:16:18 arpeggio rtkit-daemon[1493]: Successfully made thread 6226 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:16:18 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:16:29 arpeggio rtkit-daemon[1493]: Successfully made thread 6229 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:16:29 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:16:48 arpeggio rtkit-daemon[1493]: Successfully made thread 6237 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:16:48 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:16:56 arpeggio rtkit-daemon[1493]: Successfully made thread 6239 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:16:56 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:17:01 arpeggio CRON[6242]: (root) CMD (   cd / && run-parts --report /etc/cron.hourly)
May 13 08:17:04 arpeggio rtkit-daemon[1493]: Successfully made thread 6244 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:17:04 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:17:25 arpeggio rtkit-daemon[1493]: Successfully made thread 6254 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:17:25 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:17:37 arpeggio rtkit-daemon[1493]: Successfully made thread 6264 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:17:37 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:17:50 arpeggio rtkit-daemon[1493]: Successfully made thread 6266 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:17:50 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:06 arpeggio rtkit-daemon[1493]: Successfully made thread 6269 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:06 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:15 arpeggio rtkit-daemon[1493]: Successfully made thread 6271 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:15 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:27 arpeggio rtkit-daemon[1493]: Successfully made thread 6275 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:27 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:31 arpeggio rtkit-daemon[1493]: Successfully made thread 6277 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:31 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:43 arpeggio rtkit-daemon[1493]: Successfully made thread 6279 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:43 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Successfully made thread 6290 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Successfully made thread 6292 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Successfully made thread 6294 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Successfully made thread 6296 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Successfully made thread 6298 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Successfully made thread 6300 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Successfully made thread 6302 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Successfully made thread 6304 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Successfully made thread 6306 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Successfully made thread 6308 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Successfully made thread 6310 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Successfully made thread 6312 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Successfully made thread 6314 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Successfully made thread 6316 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:53 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Successfully made thread 6318 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Successfully made thread 6320 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Successfully made thread 6322 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Successfully made thread 6324 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Successfully made thread 6326 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Successfully made thread 6328 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Successfully made thread 6330 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Successfully made thread 6332 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Successfully made thread 6334 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Successfully made thread 6336 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Successfully made thread 6338 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:18:55 arpeggio rtkit-daemon[1493]: Warning: Reached burst limit for user '1000', denying request.
May 13 08:18:57 arpeggio rtkit-daemon[1493]: message repeated 2 times: [ Warning: Reached burst limit for user '1000', denying request.]
May 13 08:19:20 arpeggio rtkit-daemon[1493]: Successfully made thread 6346 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:19:20 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:19:26 arpeggio rtkit-daemon[1493]: Successfully made thread 6349 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:19:26 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:19:39 arpeggio rtkit-daemon[1493]: Successfully made thread 6404 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:19:39 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:19:52 arpeggio rtkit-daemon[1493]: Successfully made thread 6439 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:19:52 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:20:17 arpeggio rtkit-daemon[1493]: Successfully made thread 6449 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:20:17 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:20:29 arpeggio rtkit-daemon[1493]: Successfully made thread 6452 of process 4838 (n/a) owned by '1000' RT at priority 2.
May 13 08:20:29 arpeggio rtkit-daemon[1493]: Supervising 7 threads of 3 processes of 1 users.
May 13 08:12:58 arpeggio dbus[483]: message repeated 2 times: [ [system] Reloaded configuration]
May 13 08:21:09 arpeggio dbus[483]: [system] Activating service name='org.freedesktop.hostname1' (using servicehelper)
May 13 08:21:09 arpeggio dbus[483]: [system] Successfully activated service 'org.freedesktop.hostname1'
May 13 08:23:25 arpeggio AptDaemon: INFO: Quitting due to inactivity
May 13 08:23:25 arpeggio AptDaemon: INFO: Quitting was requested
May 13 08:23:37 arpeggio dbus[483]: [system] Activating service name='org.freedesktop.systemd1' (using servicehelper)
May 13 08:23:37 arpeggio dbus[483]: [system] Successfully activated service 'org.freedesktop.systemd1'
May 13 08:05:03 arpeggio rsyslogd: message repeated 7 times: [ [origin software="rsyslogd" swVersion="7.4.4" x-pid="478" x-info="http://www.rsyslog.com"] rsyslogd was HUPed]
May 13 08:23:37 arpeggio rsyslogd: [origin software="rsyslogd" swVersion="7.4.4" x-pid="478" x-info="http://www.rsyslog.com"] exiting on signal 15.
May 13 08:24:05 arpeggio rsyslogd: [origin software="rsyslogd" swVersion="7.4.4" x-pid="479" x-info="http://www.rsyslog.com"] start