My 92 400E intermittently does the same thing.

It seems to do it less after I liberally lubricated the latch mechanism.

I will eagerly watch this post in hopes that someone has a straight-forward answer for us!

You lock the car and everything indicates it is locked, but you can pull the door handle and it opens right up. My alarm will sound if I open it while it is locked...

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02 S500
92 500SL
92 400E (Sold)
87 300E (Sold)
83 300D Turbo (Sold)
75 300D (Sold)
74 240D (Sold after 20 years)