The ebuild shouldn't pass -DQTC_ADD_EVENT_FILTER=true to cmake, as it current does, or at least make it possible to switch it off and ideally also warn the user that upstream doesn't recommend it. There are two known problems with it: 1) It causes Firefox crashes. 2) It causes annoying dummy window to pop up under non-kwin WMs (see the "strange bug in GTK2" thread at http://www.kde-look.org/content/show.php?content=40492 -- I don't see a way to link to it directly, unfortunately). Upstream will reduce this one in the next version, but 1) is still serious problem. Reproducible: Always
Fix in cvs.