I guess it boils down to interpretation......
If we are referring to section 8.3.12 para e of the OM-A, that needs to placed in context, ie the aircraft is in flight.
Conversely, should the section be taken literally without context, then neither the redcap, nor the engineer are permitted in the flightdeck. I don't think that was the intention hence my belief that context applies.
Or have I missed something?