While not familiar with the intricacies of the B747 doors certainly the "plug" effect would be protective against the door opening when pressurised it brings to mind a situation that occurred many years back on another type of pressurised airliner.
Briefly, a particular door was written up many times for making air loss noises in flight but because it was a plug did not cause drastic pressure loss. No amount of re-rigging or adjustment resulted in rectification. UNTIL an apprentice airframe fitter noted that the door seal had been installed back to front so that when pressure came on instead of self sealing the seal was unseated and allowed escape of air. Murphy's Law again!!!................but it couldn't happen now could it?
