Commit 64b2b4a7d4 changed the monitor layout handling, resulting
in some layout errors due to a subtle change in memory handling:
when zooming a window in the overview, the available zoom area is
calculated by subtracting the panel height from the primary monitor
area. This area used to be a copy of the monitor rect, but as now
the rect itself is returned, zooming a window on the primary monitor
repeatedly modifies the monitor rect, leading to layout errors in
various parts of the shell.
Fix by using a copy when calculating the available zoom area.
https://bugzilla.gnome.org/show_bug.cgi?id=654105
8d1b7962d8