Interesting. Have you tried lowing the graphics all the way down and playing it. Do you get any corruption at lower graphics setting? Problems like your describing are usually caused by out of date drivers or video cards that are having trouble with our renderer.
"No man can be a pure specialist, without being in a strict sense, an idiot."
- George Bernard Shaw
"Remember, every time a April Fools joke is played, a point-n-click adventure game concept is killed."