I've had issues with Futaba s-bus decoders and savex servos.

i found whenever I powered up the receiver, ALL the servos would jitter. You would have to cycle the power and then the second time, it would usually behave.
i was using them in a model with 14 of the savox mini servos. I'd initially thought I had dodgy decoders, as I'd bought them when I was in Hong Kong, so I grounded the decoders.

reading this thread has made me think there maybe wasn't anything wrong with them.