I've found that this bug is actually triggered by upgrade of libgtk2.0-0, not xfce4-panel. Version 2.21.0-1ubuntu2 is affected, and version 2.20.1-0ubuntu1 isn't.
I've found that this bug is actually triggered by upgrade of libgtk2.0-0, not xfce4-panel. Version 2.21.0-1ubuntu2 is affected, and version 2.20.1-0ubuntu1 isn't.