Cutting both wires - doesn't it need the black -ve wire to give a reference for the signal? I've used locktite and epoxy on those HK units but it's only since using a second grub screw that they seem secure. I have to admit I haven't had a problem with them locking out on 4 cell nimh. Might be worth checking whether the mounts are out of line and distorting them by slackening off the mount screws to see if they lockout easier.
As for SBus, it doesn't affect whether a slaved channel is affected by trim. On Futaba that is set by the 'link' option in the mix if I remember right, on the Taranis it's a tick box on the mix screen. What Sbus seems to be is the complete stream of pulses for all channels sent down the SBus wire, then either the SBus hub separates out the individual channels or if you are using SBus servos the servo is programmed to pick out the right channel from the stream. For instance I'm using the FrSky Sbus hub to drive channels 9, 10 and 11 so I programmed the SBus hub to send ch 9 to the first connected servo, ch 10 to the second servo and ch 11 to the third servo - ch 11 is my gear channel so I can use the ch 5 plug on the receiver for another battery connection. Ch 9&10 are the inner wheel doors set up on the gear switch but with a delay on 'up' movement to allow the retract to fold. I couldn't do anything like that with my old FF9 Futaba.