I'm with the fall off no - remove after locking crowd.
Ours are the same way - if you hang onto them after you open they will stay in place - but turn them or lift them too high and they will come out of the track.
I would venture a guess that they were made that way - most of the compartments on the older coaches were for running gear tools, water and electic - so the last thing you want is a door that you have to hang onto and fandangle with while trying to get to the things you need.
Notice all the newer ones have drop down hinged doors - might have been a new invention for aistream
Just never occured to them in the late 60's early 70's hmmmm