If you think about what the RX would be seeing.

First the RX receives a signal that is FM modulated (most radios). This signal is slightly being shifted in frequency based on the controls your inputing with your thumbs. Now a second signal pops up that is also slightly shifting but based on totally different thumb inputs. This will obvious confuse the RX since it cannot pick out one signal from the other and would not respond to either control but the combination of the two thus erractic behaviour. I don't see how one TX could override the other one in the case of the stolen plane. Seems to me it would take significant distance (maybe 3 miles) to attenuate the signal so as not to cause interference and erractic behaviour of the plane but this is all just my $0.02.

Also, what about intermodulation. Two signals offset from your channel that cause a 3rd order product to show up in your band. I guess the quality of the RX is all that would help prevent that. Does anyone have any information on this?