Are you using Release Candidate 1? If you're using a beta, that might be related to the un-fixed problem in resizing the map editor. I can't reproduce the problem here. At one time it seemed that I couldn't have more than about 10 DirectX windows up (DirectX windows include tile previews, sprite previews and map editors), but I just loaded 5 map editors and 8 preview windows all at once without a problem. I also tried displaying layer properties windows at the same time as having multiple map editors active. I don't see any problem. But if you are using a beta version, and you have your windows maximized, it's possible some resizing happened (and an error related to it) when the layer properties window closed. If that's not it, maybe you could check if there's some repeatable process based on the sample project that could reproduce the problem. If so, describe how I could try the same thing.
