This patch fixes it for me. It looks like an upstream bug, I'll report it there.
--- gnome-python-desktop-2.28.0/wnck/wnck.defs~ 2009-10-04 16:47:54.395088780 +0100 +++ gnome-python-desktop-2.28.0/wnck/wnck.defs 2009-10-04 16:49:53.571088440 +0100 @@ -100,7 +100,7 @@ ) ) -(define-flags WindowState +(define-enum WindowState (in-module "Wnck") (c-name "WnckWindowState") (gtype-id "WNCK_TYPE_WINDOW_STATE") @@ -121,7 +121,7 @@ ) ) -(define-flags WindowActions +(define-enum WindowActions (in-module "Wnck") (c-name "WnckWindowActions") (gtype-id "WNCK_TYPE_WINDOW_ACTIONS") @@ -184,7 +184,7 @@ ) ) -(define-flags WindowMoveResizeMask +(define-enum WindowMoveResizeMask (in-module "Wnck") (c-name "WnckWindowMoveResizeMask") (gtype-id "WNCK_TYPE_WINDOW_MOVE_RESIZE_MASK")
