I can candidly say that I've never, ever, had that problem. Even with weedeater conversions and an RCGF 26. If I had an engine that would not shut down with the idle trim I'd be doing some investigation and probably some repair work. It sure would not go to the field that way. Perhaps a different carb?

If the power is not interrupted but the signal is the engine cut doesn't work. If the failsafe isn't programmed for idle RPM in the evnt of signal loss the throttle may remain at any throttle setting while the ignition cut remains asleep. Likely the throttle will remain at the position last used. Plan for the worst in those events. Set up the failsafe for an idle or idle cut off. Set up the engine itself where it can be manually shut down with the idle trim lever. If that can't be done, fix the engine. If you install an ignition kill do not use that as the primary means of engine cut off. It's still an additional safety device. Anything electrical, or mechanical, can fail. A very good reason to never, ever, remove the throttle return springs from a carb. They work real well if the linkage fails.