I'm with Geo in thinking it's a combination of events that lead to this. In the event of a jam, which is displayed on the op panel, all power to motors should be cut off. Also, opening a door should cut 24 volts everywhere. Neither of these factors is causing the motor to shut off. The fact that it's running in reverse I believe is due to it pulling any pages back from the bridge unit, so they're not torn when trying to open the bridge.
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