The problem starts happening with the following upgrade (and goes away with the corresponding downgrade):
[UPGRADE] gtk2-engines-pixbuf 2.20.0-0ubuntu4 -> 2.21.0-1ubuntu2 [UPGRADE] libgail-common 2.20.0-0ubuntu4 -> 2.21.0-1ubuntu2 [UPGRADE] libgail18 2.20.0-0ubuntu4 -> 2.21.0-1ubuntu2 [UPGRADE] libgtk2.0-0 2.20.0-0ubuntu4 -> 2.21.0-1ubuntu2
The problem starts happening with the following upgrade (and goes away with the corresponding downgrade):
[UPGRADE] gtk2-engines-pixbuf 2.20.0-0ubuntu4 -> 2.21.0-1ubuntu2
[UPGRADE] libgail-common 2.20.0-0ubuntu4 -> 2.21.0-1ubuntu2
[UPGRADE] libgail18 2.20.0-0ubuntu4 -> 2.21.0-1ubuntu2
[UPGRADE] libgtk2.0-0 2.20.0-0ubuntu4 -> 2.21.0-1ubuntu2