I can confirm this behaviour on an up to date feisty. Additionally, it only happens when you launch gimp from a terminal or the "run application" tool. Presumably this is because using the Gimp menu item launches "gimp-remote-2.2 %U" and not just "gimp":
Window manager warning: Buggy client sent a _NET_ACTIVE_WINDOW message with a timestamp of 0 for 0x2c025d7 (The GIMP) Window manager warning: meta_window_activate called by a pager with a 0 timestamp; the pager needs to be fixed. ** Changed in: gimp (Ubuntu) Status: Unconfirmed => Confirmed -- Starting gimp casues metacity warnings https://launchpad.net/bugs/91085 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs