I can confirm that when it happened to me, I had gdm as login manager and not lightdm.
Since the upgrade to 14.04, it happened just one time in one laptop (solved by login/logout) with Ubuntu Gnome, and never in my other laptop which has Xubuntu.
So for me it is happening now very rarely; last time I seen it was more than a month ago --- I can't remember. My guess is that the DBUS connection between udidskd and the desktop get lost, or stuck. Probably related to the DM, yes. Would not be surprising if lightdm and gdm share some bug.
I can confirm that when it happened to me, I had gdm as login manager and not lightdm.
Since the upgrade to 14.04, it happened just one time in one laptop (solved by login/logout) with Ubuntu Gnome, and never in my other laptop which has Xubuntu.
So for me it is happening now very rarely; last time I seen it was more than a month ago --- I can't remember. My guess is that the DBUS connection between udidskd and the desktop get lost, or stuck. Probably related to the DM, yes. Would not be surprising if lightdm and gdm share some bug.