I'm going to make an assumption here. My only pass experience is with Disneyland that does not do MB. When you go to DL or DCA and use your pass for the first time they scan it and then take a picture of you. When you park hop or use the pass again they can verify it is you. I am going to assume it was not just scanning, but no photo was popping up to make sure the person and the pass matched.
As one of the other posters had commented, about social media spreading like wild fire. I am willing to bet with social media posting the issue, there would be some less than scruples people trying to enter on a bogus ticket.
It is interesting that MB worked, so it was just the ticket system glitch. So, who uses Tickets at WDW? I did my trip, we got MB sent in the mail. So. Huh.