It happens if signal is given green and guard also signals LP will start. Some times LPs will give horn when lot of passengers are still standarded on PF near the loco GS coach and slowly pulls. When I was travelling in Janmabhoomi exp in July this year a 2 wheeler is loaded in front Parcel coach in intermediate station and the coolies on PF didnt even close the door but LP started to move the train. They quickly pulled the door when in running and there is no lock. Couldn't understand why he did it, when accidently the 2 wheeler falls down it may come inbetween PF and train coach.