When I bled my 190e, I had the same experience. Look at the master cylinder reservior closely. On my car there was actually two chambers to the reservior. The small rear chamber feeds the rear brakes. In order to fill this chamber, I had to top off the reservior and shake it to get the fluid to transfer. I was also sratching my head trying to figure this out for an hour. I bet yours is the same.
BTW. Pressure bleeding is the way to go.