because that's not implemented on metacity? see bug
https://bugzilla.gnome.org/show_bug.cgi?id=578409
** Bug watch added: GNOME Bug Tracker #578409
https://bugzilla.gnome.org/show_bug.cgi?id=578409
** Changed in: metacity (Ubuntu)
Importance: Undecided = Wishlist
** Changed in: metacity
** Attachment added: Dependencies.txt
http://launchpadlibrarian.net/36823732/Dependencies.txt
** Attachment added: ProcMaps.txt
http://launchpadlibrarian.net/36823733/ProcMaps.txt
** Attachment added: ProcStatus.txt
http://launchpadlibrarian.net/36823734/ProcStatus.txt
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