I did mention in my reply that passengers could still egress, that was never denied.
But the point has been fully backed up here. There is an isolation stopping an electrical communication going between the units, yes this is only stopping door release communication but its still an isolation. As you say everything else works. This in essence locks the rear set up with passengers unable to board or alight from that set whilst the TUDI switch is in use. That is a fact.
I dont think there is any other way but to describe it as the rear set being locked when using the TUDI switch - factually it is locked as the doors wont open when door release is commanded from the other unit.
If you were on a 10 car IET stopping at a short platform (like Ivybridge), the rear 5 coaches will remain locked with passengers in essence trapped in there unable to alight. This is the same concept as the TUDI switch as the doors have been electrically isolated by the TMS so that when a door release is commanded, the doors will not open. Again, the doors are not physically bolted shut but you cannot open them to alight as there will be no door release in that set.