Strange mouse behaviour problem

I have a strange problem whereby the mouse click is not registered if the mouse is not moved. I have concluded that it’s because the mouse does not call a RollOver on the movieclip button. i.e. because it stays in one position on the screen.
Is there a way around this, with perhaps a hitest for example?

Here is the .fla with the problem duplicated

http://www.fileqube.com/shared/OCpoWOeS126923

Thanks in advance