What a load of hot air.
My FIC buddy and I did this during our Instructor Course several years ago. No probs with any light aircraft with that type of door, as far as I have ever experienced. You may need to yaw to shelter the door to close it on some (BE-76 twin and it takes two of you - popped on take off) or slow down a bit.
Note - the IAS when you do it on the left door drops to about 20KIAS as you open the door further. The C150 Aerobat can be flown with the doors off in the summer if you wish (no FOD or loose articles). As for falling out - please... if you have on your harness or lap belt, where is the difference between that and a weight-shift microlight.
I would also open my door during a RTO exercise go give a sudden noise and rush of air, as well as EFATO at 150' to touch and go (Brief being "I will stop for loud bangs, control problems, engine fire or failure, blocked runway or smoke in the cockpit putting any burning components downwind turning L/R onto a target heading of XXX). How many PPL's have an action plan to get out little Jonny from the back and forget that if they don't turn downwind they will burn their legs during evacuation???
Better practice these things with a good QFI than experience them the day you panic and it kills you and all the POB.
Why not ask to carry out a few extra things on your next check - you may just learn something rather that preach what you have little experience of.
Anyway back to the tech bit -
It would be interesting to stick on with tape 6 or so 4" bits of string to see what happened to the flow. My guess is that (with the fact that I saw the IAS bleed off) the slipstearm is deflected causing a High P - or stagnation area. This will in turn:
1) increase the High / Low ratio between the wings making the opened door wing have a higher pressure differential and thus more lift on the opened door side.
2) speed up the airflow over the wing from the deflected airflow and increase the Low P and lift.
Anyone add anything??