I switched now to Ubuntu 8.10 (AMD64) and noticed, that the VASmalltalk windows are able to produce refresh/redraw problems on other windows. As an example:
If I move the window "vast - Datei-Browser" around (within the area of) the VA Organizer window you may see the black rubbish at the edges. This is not only limited on GTK-windows, but this also happened to VA windows itselfs (here its even worse) - the reason seems to be the "black" lines within the windows.