I'm not sure what exactly is going on, or if it's a bug or me doing something wrong, but I figured I'd post it and find out.
What's happening is, at complete random, both of the preview windows will mess up. First, the smaller one on the left (I can't for the life of me remember what it's called) will turn in to a kind of stretched 3D side preview thing, then shortly afterward, as I play with any of the settings of any of the shaders, the 3D preview window will maximize to the biggest it can get.
This hadn't ever happened to me on the free version, but now that I have regular Deep it is, if that helps at all.