Shouldnt that be considered normal??? The initial light up of the oil light is standard to just about every car - self diagnostics to say the sensor and cicuit is operational. And a few seconds after car is up and running, oil light goes OFF, if the level/pressure is fine as the case may be.
Oil light STEADILY LIT, that is a different problem. That means you are low on oil and need to replenish; or oil sensor is stuck.
RE: oil sensor probs - I've seen this happen in many bimmers, especially those cars that haven't been serviced on a regular basis.,, esp the oil changes.
The oil sensor is pretty much like you toilet bowl float. it rises up and down a shaft along with the current oil level.
Over time, sludge builds up in the shaft and gets stuck... If it does get stuck in the lower levels, thts when u get the oil light. In really dirty engines, it takes a little time before it "unstucks" itself so it can play freely. Or as the shops like to declare "REPLACE"....