You are correct in that you have to reset the system. You do select the tire size while parked but you have to drive the car for it to "learn". (I believe the manual says you must get to something like 16 mph. I don't have the manual handy.)The only way to reset the system completely seems to be to deliberately select the wrong tire size in the menu (you have to be parked, can't do this while moving), let it "learn" for a few minutes, and then switch back to the correct size.
Kind of lame. I just had to do this last week to get it to recognize a new set of tires properly. Maybe that'd help in your case?