Hmm, I find that very odd then unless there is a problem with your video card. Out of curiosity, have you tried deleting the work unit to force a request of a new one? I had an issue the other day with a certain WU causing unstable machine errors even on stock settings. I ended up having to delete it since my machine didn't like it for one reason or another and I was fine after that.
it's been like this as long as I've had the set up. it's never been useable with GPU and SMP running flat out, too much lag on even basic things