My m104 engined 124 car did this, though perhaps not to the degree you describe. My assumption (guess?) is the thermostat is a bit slow to open when it has hot water on one side (engine) and cold on the other (radiator hose). I always saw the temp guage rise a bit above the normal point then settle back down. For example, the engine always sat at 82c in cooler weather; it might rise to about 90c from a cold start, then drop to 82c and stay there.