To be honest it's a bit more complex than that. Depends on the stock but Bombardier trains in general do have quirks. Panels can be live on Turbostars with no key on, eg. adjacent panels in the same coach on a 171. On Electrostars the panel controls can definitely be live without a key on - obviously a fault but I've found it at least three times. In addition you can use the starter bell with the key off in the first few seconds after the associated local door has closed, which is a design feature not a fault.
I've never been told to take a train out of service due to a fault with a single panel. Multiple ones will be a different matter, and likewise if controls are live but insecure through lack of a lockable door. To the best of my knowledge there are no door release controls on Electrostars which can be left active without a key of some description, as the door panels don't have those, so you're unlikely to be able to break interlock without doing something else.
Panels may be used by conductors by insertion of the relevant key. No provision has been made in the instructions for conductors about the panels on 387s not being able to be used at certain times. If conductors are to operate the train then they would have to be briefed if an active panel, in error or otherwise, could interfere with operation - DOO services can be picked up by conductors and worked from intermediate stops, eg. Gatwick / Dorking / Leatherhead / Selhurst / East Croydon. No traction knowledge requirements have changed from 377s, where an active panel can only interfere with operations when it selects a local door for dispatch. Therefore it is to be assumed that faults and failures can occur with the panels at any point.
