Created attachment 318645 [details] test add-on When you give a button a tooltip inside a panel, that tooltip will not display until you give that button focus. After that, the tooltip works just fine. The test add-on attached adds a button to demonstrate this to the statusbar.
Shawn, do you still see this bug? I don't. I tested with your "overlay from add-on".
It's possible my test case works - I'll get back with you to verify though.