Here's a short video I just uploaded which illustrates my problem. Random parts just disappear when moving the cursor over them in an assembly.

http://www.youtube.com/watch?v=VDd_J8tUhMk&feature=youtu.be

I'm using SW 2012 SP 4.0 on Windows 7, being emulated with Parallels on a Mac Pro (32GB RAM, 2 x 2.93 GHz 6 core Intel).