Comment 1 for bug 802747

metacity 1:2.30.3-0ubuntu8 altered the patch to set the "capture-before-unmap" gconf key to false by default. Check if your gconf setting for this is on, and if turning it off resolves the problem as well as disabling the patch entirely does.

If so, then I think all is good. Only people who deliberately turn on the option, or who upgraded during development when the switch was on by default, will see the problem.