I've seen a few threads in the past mention that players with newer-series Radeon cards have been experiencing a lot of graphical issues - things like repeating textures on pickups and broken particle effects from lights. Like this or this. I've been having these issues myself over the last few months, on my fairly new Radeon R9 270x card.
Recently I've noticed that there seems to be a specific trigger for these graphical bugs to start happening - witnessing the death of a Super or Ultra Blast Cube. Seems ridiculous, but I think the sudden spawn of a bunch of explosive gel balls is causing problems. When I play multiple levels in a row that don't have Blast Cubes spawning anywhere on the map (such when I was farming Candlestick Keeps back in the last Kataclysm) these bugs never show up, but when I play a Slime level or danger room where they show up, these issues start to crop up until I re-client.
What I'm wondering is if anyone else who is using a 7000 / 8000 / R200 Radeon card has that issue with Blast Cubes, too, or if their graphical issues with the cards start to come up some other way (which is probably the case.)
Try instaling new driver http://support.amd.com/en-us/download click auto detect and download lastest version of video driver