Argh. I'm sorry to bump this again, but I wanted to reply before I went to bed for the night. I don't think setting the affinity totally solves the issue, if at all. I'm having the same problem again and the issue seems to appear when I hit the maximise button on the top right of the window (I play in non fixed windowed mode). Am I being a complete noob? I like to play in this mode because it allows me to easily see the taskbar and switch between wow instances.