Have had same experiences with my old '80 240D and now my '89 300CE. "Normal" operating condition (on those cars) is for the guage to come up to max after startup and stay there while driving (moving). At a red light or other stop, it will drop down between the "1" and "2" mark, then max out again upon acceleration. I've noticed that when I put the shift into neutral, while at a stop sign, the economy meter drops to a lower level (indicating less fuel usage), and the oil pressure guage goes up slightly.
Just a guess, maybe not a good one, do you have too much oil in the engine? Too much oil will increase the pressure, resulting in damage eventually.