Multi Screen coordinates grabup problem

I found a bug on grabup, can someone try to fix it, I'll verify if it works:

I work on a 4 monitors desktop. The main screen is in the middle 'cause the side one's are connected by a pci video card.

Here is the problem, grabup take the lefttest screen as coordinates 0-0 so all the screen shot are wrong, I solve temporaly the problem by setting the leftest screen as primary.

Could someone help me please?

Thanks
Juheur