I had a door come open twice in the same flight on an R22 based in LA. I was on my way back to long beach from french valley flying solo when the passenger door came open...twice! The door was securely closed and over a period about two minutes the catch managed to creep up and open! I reached over, locked and latched it and carried on back to Long Beach. I was at about 80kts at the time but had no difficulty shutting the door. I reported it as a fault when I got back to base but left LA before the aircraft returned.
I've flown lots of R22's and R44's both old and new and have never had it happen since.
CRAN