The reason for the hidden tab to show up are the required fields and thereby the enforced processing sequence in filling out the tab strip fields.
If you check the tab caching indicator upon entering the screen, it's going to be red, then turning green once you entered the required fields in the Notification tab. So essentially tab caching fails first which results in the unwanted rendering of the tab strip.
I'm afraid there is nothing you can do about changing this behavior. Required fields are often the cause for tab merging issues. You'd have to get rid of the required fields (make them optional) in order to fix the problem.