I have a 2004 E500 with dynamic seats. The lumbar support inflates randomly this portion of the seat isn't included in the dynamic seat sequence, it is only part of the message sequence - Both of which are off!! This is very annoying and I would consider disabling the feature but the only fuse that appeared to be associated with this feature was the "pneumatic seat" which I removed and still the lumbar support inflates randomly or via the seat control.

 

Sounds like there is a malfunctioning switch/controller somewhere. Can you take to a dealer and ask for warranty coverage of the repair?