linuxmint/Cinnamon — pull request #781 by mtwebster (2012-06-18 00:59:27+00:00)
Title: Partially address #731 - left-clicking will cancel a drag if you've

started one, then gone off a panel and released the mouse button -
the DnD handler is left in an incomplete state - it doesn't know
you released the mouse button, and assumes you're still in the middle
of a drag.

the DnD handler doesn't track events outside the panels, so unless
this is changed, there's no way to absolutely fix this problem,
though it is an annoying one.