Confirmed in kde4.1.1. I had gtk-qt-engine-kde4 and gtk-qt-engine installed.
Purging gtk-qt-engine removed the conflict. Gimp and Firefox then started as expected.
Confirmed in kde4.1.1. I had gtk-qt-engine-kde4 and gtk-qt-engine installed.
Purging gtk-qt-engine removed the conflict. Gimp and Firefox then started as expected.