I'm a bit tired to poke through all posts here, but what came to my mind is this: the signal from the antenna on 2.4ghz systems is projected out the side of the antenna, not directly out the top. One is never to point the antenna directly at the model as it will be in a 'blind spot' so-to-speak. The antenna is to be pointed straight up as one is generally not to fly a plane directly over his head. If the antenna was placed on the ground and pointed at the plane, the plane would be in a dead spot and lose signal, thus going into fail safe. I'm wondering if the radio being on the ground was deflecting signal off the ground and thus enlarging the dead spot. Anyway, that's my theory.

And yes, why on earth would you put down a radio to a running plane? Let's hope this is a lesson learned, and the OP and whoever else reading this thread never does this again.