Once all my pieces are in my home square (and only then) I can no longer move. When I try to click on either a stone or a menu item, the whole window moves by about the thickness of a point and the click has no other effect. If I moves the mouse pointer over the object in its new position and click it, the window jumps back to its original position with no other effect.

I can't even exit through the file menu because it won't stay still.

It is a new installation and I am the only person to have used it, so it is not some weird joke program, and it only happens in GNUbacgammon. 

This is not a joke; though it sounds like it. I have previously used GNU bg before (possibly an older incarnation) without any problem.