I cannot remember exactly where I saw it, but IIRC one of the sanctioning bodies maybe AMA? Came out with a directive to remove all onboard propane systems?

Maybe it's just old guy memory issues, but I know lots of guys removed the propane tanks from their models and that is supposedly why. It is a real fire hazard since it's so easy to light the stuff, if it leaks into the model things could go bad real quick.