Very strange indeed! Did you plug the test servos directly into the receiver channel 3? I assume that there isn't an extension (possibly bad) that is always in the channel 3 path.
ORIGINAL: discusmike
Also,i had atleast five flights with the first reciever,then the throttle stuck,i landed the plane,and the trottle worked fine,we could not figure it out,then we flew the plane a couple of more times incident free,then the throttle stopped again,this time it would not work at all after landing,we plugged other servos into channel three and none worked,but when plugging the throttle servo into other channels it worked fine.