Version:           unknown (using 4.2.00 (KDE 4.2.0), Arch Linux)
Compiler:          gcc
OS:                Linux (i686) release 2.6.28-ARCH

Since my upgrade to 4.2 my full screen windows begun flickering whenever, for example a notification popup appeared. It's especially annoying when I watch fullscreen movies or use gwenview.

Way to reproduce:
1. Open gwenview
2. Open a file
3. Click "Full Screen Mode"
4.a.1 Hower over "Configure Full Screen mode", wait for the tooltip
4.a.2 Wait for the tooltip to appear, before that the whole screen flickers with the background similar to the one that's upon KDE startup
4.b.1 Click on "Configure Full Screen mode"
4.b.2. The whole desktop will flicker before the toolbox appears much the same as in 4.a.2

I'm using Arch Linux with the following specs:
Kde 4.2
xserver 1.5.3
nvidia 180.22 and 180.29