Version: 4.2.2 (KDE 4.2.2) (using 4.2.2 (KDE 4.2.2), Kubuntu packages) Compiler: cc OS: Linux (i686) release 2.6.24-24-generic When part of e.g. the KDE help center window is covered by another application window and then brought back on top, the window is often partly filled with "noise". Doing something like highlighting/selecting the text causes the display to be redrawn correctly. While submitting this bug I noticed this happens with Konqueror too.
I suspect this was a bug in khtml, or anyway related to the underlying graphics system. Closing, please reopen if still relevant.