When a 3d window is moved by a certain delta, DRICopyWindow takes
the current set of cliprects and copies them to their current position plus
This is incorrect as the cliprects will obviously change when the window
is moved. It is necessary to take the destination cliprects into account
when copying regions.
This can be easily seen by running say gears and isosurf at once, and
moving the isosurf window around *underneath* the gears window. Bits of
isosurf will be visible in gears.