Comment 22 for bug 987858

I have the same problem. It seems that it only appears when the network interface receives an IPv6 address.
"sudo service network-manager restart" helps slightly, but not completely.

** (nm-applet:1438): WARNING **: Could not create object for /org/freedesktop/NetworkManager/IP6Config/1838: Method "GetAll" with signature "s" on interface "org.freed
esktop.DBus.Properties" doesn't exist

** (nm-applet:1438): WARNING **: Could not create object for /org/freedesktop/NetworkManager/IP6Config/1923: Method "GetAll" with signature "s" on interface "org.freed
esktop.DBus.Properties" doesn't exist

** Message: NM disappeared
** Message: NM appeared

** (nm-applet:1438): WARNING **: Could not create object for /org/freedesktop/NetworkManager/IP6Config/7: Method "GetAll" with signature "s" on interface "org.freedesktop.DBus.Properties" doesn't exist

** (nm-applet:1438): WARNING **: Could not create object for /org/freedesktop/NetworkManager/IP6Config/143: Method "GetAll" with signature "s" on interface "org.freedesktop.DBus.Properties" doesn't exist

...and so on.
After restarting NetworkManager is no longer occupies 50-100% CPU, but still not 0.
  PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
23059 vk 20 0 943m 142m 20m S 8 4.7 0:11.36 chromium-browse
13465 root 20 0 255m 7456 4424 S 5 0.2 0:23.58 NetworkManager