Steps:
1. Open an application with headerbar (e.g. System Monitor)
2. Click a focusable widget inside the window (not in the headerbar)
3. Press the Tab key
4. Try to move the focus back inside the window, out from the headerbar

Expected:
One should be able to cycle through all the focusable widgets using the tab key, shift-tab and arrow keys
What happens:
Once the focus gets in the headerbar (and it does that by first Tab keypres), it will not get out of there without using the moust.