Any luck solving this problem? I was experiencing this problem in Unity 4.1.4 at random times. But now in Unity 4.2 every time I hit Space to maximize the Game tab and hit Play the problem appears. It’s really annoying since I have to close the Editor and reopen it.
In my experience, the bug is due to you changing the GUI.Skin font in your code. This might not be helpful, but at the end of your GUI code try changing the font back to the default font and see if that works.