The report said that there were "many" doors open, not sure if that was true or not. If there were more than one set open it's puzzling why they weren't all open as they all open at a station, unlike on NR where the pax have to press a button to open them.
If it's only one set it would still have to be 2 failures. The failure of the door closing system and also the detection system.
Incidently, but slightly related to this, IIRC a while back there were problems with some new TfL trains where the acceleration was such that the doors were coming open slightly and it was cutting out the motors.
Although I know it's not good to speculate, my money would be on human error with this one. The idea that the technology alone would allow this is serious in the extreme and would surely lead to a "drains up" on the type of stock involved.
There are a couple of obvious possibilities.
If we assume the interlock switch has been operated, which unless there’s been a wrong-side failure MUST have happened.
If the train has already been taken out of service due to door problems that would give us a reason for the switch to be operated. All we need then is a reason for the doors
to be open unknown to the driver. Perhaps confusion over who has tipped out what parts of the train (although the driver should still check)? Passengers would naturally have the opportunity to unwittingly join the train if they arrived on the platform after announcements.
Another possibility is the same scenario but all the doors opening of their own accord unknown to the driver after initial tip out. He wouldn’t necessarily hear or see this if doing something else at the moment, like for example being on the radio to the signaller, and wouldn’t notice the pilot light going out as it already would have been out for a known door defect. The TBTC system can cause doors on a whole train to open without the open buttons being pressed - this certainly happens in known situations in the Northern, although it wouldn’t do it if the train was on the move. One scenario for this is at the point where the train’s destination has been altered by the signaller - again something very likely to be going on for a defective train just taken out of service.
Something like the latter is what my money’s on - it would also explain why the train isn’t very busy- supposed to have been empty and these passengers are ones who have unwittingly boarded.
But, as I posted earlier, we should keep an open mind - it could be some kind of technical failure, albeit a very serious one.