Description of problem: in current implementation of metacity, it keeps _NET_SUPPORTING_WM_CHECK property in the root window even when it's gone. usually it doesn't work properly so that the window id that property contains would be invalid. however it would affects unexpectedly when any applications grabs that window id, and any applications referring to that value will behaves unexpected thing. So I'd suggest metacity should removes it before finishing. See Bug#471927 for the unexpected problem happened without the removal of this property. Version-Release number of selected component (if applicable): metacity-2.24.0-2.fc10
mclasen's patch applied upstream before 2.28.0, should be OK in F12