I think I came close to a big accident at Ipswich in an old C150 in 1973 (one tends not to forget). I was a student practicing some short field landings. I applied the final stage of flap and let go of the switch. Shortly afterwards, I was very surprised when the aircraft buffeted and fell out of the sky, landing well short, despite me applying a lot of power (probably full throttle, thinking back). Fortunately for me I had aimed 1/3 of the way into the field as a touchdown point - if I hadn't I would have possibly been down on the main road in the undershoot.
The switch, which was worn, had flipped up through the "OFF" gate into the retract position as i released it and the flaps completely retracted themselves on short finals. I was then doing a flapless short field landing, which obviously didn't work out too well.
I had the pleasure of flying a couple of brand new Reims C152s shortly afterwards and realised the new flap operating system was much better.