Umm. I have been lucky it has never happened to me.
I did remove mine within a couple of weeks of ownership but that was due to it dropping onto the engine.
There were 5 of us in the 35 degrees of Croatia and it did not happen to any of us, even after 2 days where the cars were parked up in the heat outside the hotel.
Maybe it is a drop in fuel pressure due to age or a very small hole in the system that is too small to allow the fuel to leak. (Just a complete guess)