When I opened the reader's email Alessandro Gruetzmacher and I came across these screenshots, I thought it was a joke some really crazy screensaver or something. But it seems that the problem is really serious, probably caused by some defective graphics card.
According to Alessandro, the bug occurred twice in a row, always when he tried to switch the active program via Command + Tab. Each time the shortcut was pressed, things got worse (or improved, on the artistic side, hehe).
I'm glad I never saw anything like it here?