This happened to me in every version of Corona - I left-clicked in the VFB, and it resized. Like Romullus said this means that a single mouse click is for some reason registered as a double click.
*Maybe* this could be improved somehow, for example by adding some kind of threshold for the mouse clicks, so double click would be ignored if it's too fast, but one the other hand this could lead to the window not adjusting when it should.