Vampire sr1 glitch with steering

[Clarkie]

Hope someone can shed some light on this

I have a

sanwa 451 receiver and Gemini x
Vampire sr1+ speedo
Vampire 7.5 motor
Spektrum 6040 servo

The problem that I'm experiencing is that when you move the steering on the transmitter the throttle kicks in and out a bit.

I have tried

another receiver - fault remains the same
Another servo - fault remains the same
A orion r10 speedo - fault disappears
Vampire speedo and Servo disconnected - fault does not appear

Not sure why when the servo is connected it affects the vampire, but for some reason it does, got me puzzled

It's been fine for the last 8 months too....