This happens sometimes. It only happens when there are a lot of graphics intense things are open at once (+4 rhino files, indesign, photoshop). Other than that it is hard to predict. It happens all over my screen, and it has happened on both monitors I have running. It happens in a different place every time. Restart seems to fix. Everything is running fine besides the weird pixel annoyance. 4core, 16gb memory, D300.