hi there Colin
What speed controllers did you use when you were switching the signal on/off? because using modern day speed controllers - when you switch the signal off, and then back on, they sometimes reset themselves at Zero - wherever the throttle stick is positioned on the handset.
In other words, if you are running two speed controllers off one channel - and say you are running at half speed, you switch one of the speed controllers off (say, for arguments sake the portside speed controller) then switch it back on - where your transmitter throttle stick position is set - this will now become the midway position for the portside speed controller, if you follow what I mean
so therefore when you bring your throttle stick back to neutral for the starboard speed controller, the port one will still be running at half speed - due to the fact that it has reset itself at a different position.
In 'olden days' when the very early ACTion speed controllers & Electronize you could switch on/off quite easily using the signal wire as they did not have the technology built into them for memorising the stick position.
John