Version: 1.6 (using KDE 3.5.1, Kubuntu Package 4:3.5.1-0ubuntu7 dapper) Compiler: Target: i486-linux-gnu OS: Linux (i686) release 2.6.15-15-686 When you e.g. open the K-Menu and have a konsole laying around below it, there are sometimes repaint issues or artefacts when the menu is closed and konsole gets uncovered again. The foreground text is not painted correctly but the background color is, as it should be. In the result, that means you have a solid filled konsole, but with rectangular parts of text missing. I'm using the nvidia-legacy driver. Don't know if it happens with the F/LOSS ones too.
Please try with the free driver too - this sort of thing sounds like a driver problem.
Did you get a chance to try with the free driver?
Reopen if you reproduce with the free driver... upgrading KDE is suggested as well.