onmouseup event not firing

[avibe]

I have a document that contains an IFrame (all source items are from the same domain), when I attach the onmouseup event to a div in my IFrame it will fire when my mouse is up, no matter if I am still on the element with my cursor.But if I leave the IFrame still holding my mouse down and then release, the event is not firing.Is there some way to catch this issue, maybe know when the user it out from the IFrame with is mouse cursor