Bizarre.
I am having the same problem on a 230SL. Observing with the door open, there is no difference in the movement of the latch when the inside handle is pulled vs the outside button pushed. But with the door shut, when you pull the inside handle, the door stays solidly shut. You can put your shoulder into it and it won't budge. You would think that if there was some miniscule difference in movement, that a good shove would open the door. What am I missing?
FWIW, the lock works fine.