I am interrested in a response to this because I too have had a similar problem with my 9CAP. I run on ch45 and am using two FP-R148DF and another futaba reciever(standard) in three of my aircraft. When I would get in a specific position 15ft away, my servos will move in full deflection to one position and hold there untill I would touch the antenna(it is collapsed and this is during a range check) or walk further away. The airplane would seem to recieve well up to almost 200ft, during preflight check. It is interesting that There is only one problem at that one specific point one one side of the airplane, and another equadistant on the exact opposite side of the airplane. This is happening on all three aircraft. I then pulled the rx's out of the airplanes and did a similar range check with the exact same results, so it is not a routing problem.
Concerned it was my radio, I borrowed another rx from a friend on the same channel, hitec though, and the problem has dissapeared. I really like Futaba and have no plans to change brands, but only wanted to test to ensure if it is a radio problem or a rx problem. I think the problem is in the rx. I am interrested if I should send in all my rx's for testing, and if so, what would cause all three to all go bad at the same time, doing the same thing? They are all wrapped in good foam, so I know vibration could not be the issue.