I've been happily running Knoppix 6.7.1 off a USB stick for some time now and decided to upgrade to 7.2.0

Everything works just the same as 6.7.1, with the bonus that 7.2.0 now recognizes my iPhone so I can manipulate songs and photos. The problem is that after a period of use, typically browsing, the display (Acer Aspire 5520) starts producing strange artifacts and menus etc become hidden/unusable. Eventually I have to force a shutdown. This has happened three times in the last few hours.

When I boot to 6.7.1 again the display works as expected and does not degenerate so there has to be some difference in the two versions that is causing this behavior. Can someone here help to resolve this issue?