Hi,
I had a play around with this bug today. I'll give some speculative thoughts in case they jog the brains of anyone else who has looked into it.
I think it might be related to the fact that no LEAVE_NOTIFY (or whatever it is) is received when you move the pointer out of the window with a mouse button held down (ie in a drag). I think this might in turn be related to the fact that the masking of events is changed during drags.
The particular bit I was playing with was dragging a rectangle to the edge of the window. This produces a "freeze" which I think is what people are seeing a lot (mouse pointer gets stuck on the `move' icon, no toolbar buttons or menus work).
I then added the LEAVE_NOTIFY_MASK to the mask that is applied to events during a drag, and made the leave notification simulate a button release. This kind of fixed the problem, in that the freeze stops happening, but causes others.
Anyway I'll take another look tomorrow and see if I can come up with a proper fix. If anyone has any thoughts I'd be interested.
Cheers
Carl