This problem deserves a place in the knowledgebase if only because we posted a lot of equipment backwards and forwards before we found the solution.
The system; 2 x DNO-10, DMR-203, Ex 2.4 GHz radio receiver.
The symptoms; One DNO would consistently go into reverse for a moment and then stop. The fault seemed to be related to one channel of the DMR.
What was it; The throttle channel on the radio control receiver was not working, even though all the other channels functioned correctly.
Solution; Fitting a new receiver.