Version:            (using KDE 3.5 (RC1) Level "a" , SUSE 10.0 UNSUPPORTED)
Compiler:          Target: i586-suse-linux
OS:                Linux (i686) release 2.6.13-rc6-git13-4-default

it's just a guess that it has to do with the pixmaps really, and has only occured since the 3.5 versions, at least from alpha release on.
The thing that happens is that in kicker, when having activated a background image, hovering over some portion with a button, let's say the kmenu button or any other link to an application on the panel, the background tile shrinks into the top left corner, having 34x40px (plus minus).
Similar thing happens when using a style like ThinKeramik, which I guess uses that pixmap background; when hovering over some pushbutton, it sometimes does not draw the whole button background but only the leftmost portion, the rest stays "flat". Sometimes here means that you have to press the left mouse button first anywhere apart from the pushbutton and then hover over it. That said, I just realised that's the same with kicker. So maybe it has also to do with some dirty mouse event?

Hope that was enough description

bye M;chi