Comment 15 for bug 980159

Ok, looking into it I'm unsure if that's a gimp or compiz issue but that's not an unity,hud one, what happens is that the "gaussian filter dialog" takes the focus, when you validated the action that dialog closes and the focus go the toolbox ui (which has no menu associated to it) and not to your canvas (you can look at the decoration bar at the top of the dialog to see which one is colored).
Since the hud lists the items for the active dialog it has none for gimp in this case

The issue is not specific to the HUD, it's rather a wm,gimp interaction issue

That will be "fixed" next cycle with gimp 2.8 which use a single ui rather than the multiple dialog it's using in the current version