Just got back from repair night at the clubhouse. First order of business for me was Mustang glass-off testing to see if the short plunging auto-plunger thing was still happening. It still does it consistently on my machine. I didn't see a setting that would be related, and all of the switches are working in switch test and gameplay (i.e., it plays a sound effect when the ball leaves the bottom shooter lane switch).
I also set up a Gear 4 MB and played it out letting all balls auto plunge and picking up no jackpots. Once it was over, the Multiball light was not lit at the scoop. If Steve B. ran into a bug, it wasn't a straightforward one where simply starting the MB and not flipping is necessarily going to get it to happen.