Dear Gaieus,
I am very well aware that that would be the logical cause. These two points, however, show that it's not the actual cause:
-The Alt+space, M trick doesn't work. (I know how it works, I can succesfully apply it to other windows.)
-When hitting the View --> Shadow button, it does not get a checkmark. If the window was open somewhere, but out of screen, then it would get a checkmark, indicating you have the window open.
This is sufficient evidence. There is no window. Not even out of screen.
@unknownuser said:
It is not a problem (any kind of bug or issue) with SketchUp itself but with the OS as it handles windows (in this case, SU dialogue windows).
Since there is no window, this quote is not true. This is a SketchUp bug and should be treated as such.