That script works fine for me with the treebar on 7.72 no beta, the -z switch makes the window sits at the end of the treebar and getting the event to trigger multiple times doesn't seem to make the window go away from the treebar, it's actually possible to remove a custom window from the treebar with /window -w0, maybe that's how you got there? You'll have to give more informations about how you get the window to disappear from the treebar
