I am writing a new toolbar, with a much more minimal approach than before. One element I have reduced in size is the bag/mainmenu icons etc. However, this has messed up the pop-up menu.
I encountered the same problem. As long as they dont separate the artasset assigning between buttons and main menu icons there isn't much that can be done I'm afraid..
maybe instead of reducing the graphical elements you stack them counter sided and reduce the text box height... I haven't looked at the code yet so this is just a guess.