A creepy drawing glitch in Mozilla Thunderbird 3.1.20

I am pretty sure, that it regressed, but I still need to perform a regression-test.

Reproduction step

• install Mozilla Thunderbird 3.1.20 and run its main app, directly after startup it presents a configuration dlg
• try to hover with the mouse over the controls

Expected result
Hovering should not totally break the painting

Observed result
0.4.13-RC-40-g63f46f3_yuck.webm
0.4.13-RC-40-g63f46f3_yuck.log (shows nothing of interest)

I would be surprised if this was not related to Win32SS, stuff like CORE-16644 eventually.