Beyond belief. I've flown in the Gulf of Mexico in aircraft with 25000+hrs and doors popping open is a common occurrence. I am not sure about the bubble window, but in 206B's and LongRangers there is no need to panic (unless you did not clean up loose items in the back), just slow down to 40-60kts, put in some opposite pedal and slam it shut. If it does not latch, still no need to panic the slipstream will keep it from opening too far, proceed to landing site and close it on the ground.