A couple guys at the track had this problem with the new RX. One of the Spektrum sponsored guys said to try to bind it from a greater distance like a couple feet. He said this worked for a few of them and have had no problems since. BUT he also said if this doesn't work as well, then send it back, the receiver....
I finally gave Horizon a call and apparently they are starting to get reports of the problem, as well as seeing it on there own stuff. No fix yet - they expect there will be a new firmware release at some point to take care of it. It doesn't drop the bind once it's powered up...instead, when it powers up it 'forgets' its already bound, and just stays in the failsafe position. I don't think the distance from the transmitter to the recievers is the issue - I could see that being a fix if you couldn't get it to bind in the first place, but I had no problems with that. The old receivers seem rock solid with the DX3R, so they think the problem is in the receivers' firmware. The word is run the old receivers for now if you have them, and stay tuned for a service bulletin.