Similar problem at Shoreham a few years ago: was pax in a PA-28, I was inside sitting on the rear seat while the pilot completed the walk round: door was a little ajar when a Jet Ranger hover-taxied past fairly close - downdraught blew the door open to full extent with a bit of a bang. Pilot completed checks, all got in, closed door, and we taxied to the fuel pumps. Tried to open door.... !!!!!! Absolutely no way would it open. Fortunately the refueling guy was able to open it from the outside. Would have been fun had we not needed fuel and then ditched or crashed somewhere...
An engineer repaired it, a split pin in the latching mechanism had broken apparently...