When I am in the 'Find and open simulation' section, and I click the close button (on the window itself), it reverts to the simulation that's currently opened (the 'normal' view). I don't know if it was on purpose, but it's sort of weird. Maybe it's better to just have a close button on the list of simulations instead.
I've never played a game were that happens, but there are some apparently. Personally I agree with Awesan, when you click the X on a window it is supposed to close the window not contents.