andrew66, Bill here again. I have contacted our technician for JR Radios here in Australia, and explained your problem to him. {Idid this because i also use JR Radios} He informed me that sometimes during manufacture of these parts, a film will develop on the pins of the plugs. To clean them , just simply pull out each and every plug, and replace them . Do this , one plug at a time, in and out 3 or 4 times . All plugs that go into the receiver and any other plugs you may have , do them all. This will clear any film that may have been on the plugs, causing an arcing, which will make the servos respond as you described.
Hope this simple test will fix your problem.
Best regards , Bill , from down-under