Comment 8 for bug 334249

Confirmed here also on my Dell Vostro 1310, who was working fine before upgrading to 9.04.
Seems that it's really some X thing. When the keyboard and mouse becomes locked, it gives an error, check the syslog message:

Apr 28 13:04:29 neo kernel: [ 66.554074] [drm:i915_get_vblank_counter] *ERROR* trying to get vblank count for disabled pipe 0
Apr 28 13:04:29 neo kernel: [ 66.556092] mtrr: no MTRR for d0000000,10000000 found
Apr 28 13:04:29 neo gdm[2585]: DEBUG: gdm_server_stop: Server pid 2589 dead
Apr 28 13:04:29 neo gdm[2585]: DEBUG: gdm_slave_quick_exit: Killed everything from the display
Apr 28 13:04:29 neo gdm[2582]: DEBUG: gdm_display_unmanage: Display stopped
Apr 28 13:04:29 neo gdm[2582]: DEBUG: Attempting to parse key string: xdmcp/Enable=false
Apr 28 13:04:29 neo gdm[2582]: DEBUG: Attempting to parse key string: daemon/ServAuthDir=/var/lib/gdm
Apr 28 13:04:33 neo bluetoothd[2549]: bridge pan0 removed
Apr 28 13:04:33 neo bluetoothd[2549]: Stopping SDP server
Apr 28 13:04:33 neo bluetoothd[2549]: Exit
Apr 28 13:04:34 neo exiting on signal 15
Apr 28 13:05:31 neo syslogd 1.5.0#5ubuntu3: restart.

The restart there is when I pressed the power button, because there were nothing more to do with the keyboard and touchpad locked.