If you switch to another window while playing a world, after coming back Minecraft crashes (the window closes with no message) a few seconds later.

I first noticed this in 1.1.4 but then it only happened if you actually minimized the Minecraft window. If you left it restored or maximized it didn't have a problem.

Since installing 1.2, this workaround no longer works. Even if you leave the window restored it will crash.

The problem happens whether or not Minecraft is in fullscreen mode.