Hi I had same problems with MK, Garupner and Herkules III. After 50 good flights I started to have strange fast movements of copter in different directions without any problems in log. For now I think that was because of interference from herkules to GR-16....but I still investigating.... So one of things which I did was upgrading software in garupner mx 20 to 1.173 and in receiver gr-16 to 6a35_f9. And after that MK doesn't recognize that mx20 is switched off. The failsafe doesn't work !!! There is no information via telemtery or bluetooth that transmitter mx20 is off !!!! After downgrading to version 33508_gr_rx8_6a34_f9 failsafe started to work. So do not upgrade software in GR-16 to newest version !!!! What firmware do you use in your Graupner receivers and transmitters ?