I have owned two MB's where this Brake Pedal "Kicking" occured and I was assured that it was normal.

One of these I still own, a 190E, and every morning, going backwards or forwards, it "Kicks" a few times. My 300E was the same.

This is only the ABS pressure buildup priming the system.
It has done this from the day I bought it new nearly 20 years ago.

Mind you on my 2001 E320 CDi this does not happen ever.

Mike