This is becoming a common scenario with modern cars as many now have automatic parking brakes, no true hand brake. It’s not just Mercedes, my iD4 does the same thing when parked wet.
Strange thing is, I used to disengage the emergency brake on my GLC (if I remembered) when I came home and I avoided the problem but now even if I disengage it it will re-engage all by itself as I am leaving the car!
I do not think Mercedes will do anything about this problem for individuals, the technology just has to evolve.

 

It's a sequence issue to keep it disengaged. Stop the car and keep the engine on. Put car in Park with foot on brake. Pull out the parking brake release and hold it out. Now shut off the engine. let go of the parking brake release. Take your foot off the brake. You should feel the car roll a bit until the driveline parking pawl engages. When you open the door the electronic parking brake will not reengage.