For me, it was on the indiana Jones ride at disneyland paris. Me and my brother got on the ride, and we got to the top of the ride and it went over the top of the drop, and the restraint started to click open!!
Everytime there was negative g force, the restraits on me and my brother started to click open a bit and we had to hold them down! I don't think they would have fully opened, but it sure felt like they were going to
When we got off the ride, we told the ride-op what had happened and he checked our restriants and then the ride was stopped for a bit, while they took that train off the track to be checked over. A lucky escape I think [;)]