In cubase 8 this was not a problem. I have the MCU Pro and extender set up exactly the same. However, in Cubase 8.5 when you select a midi channel, if the record button is enabled and you move the slider it will make the sound of the instrument and it will forever pitch alter the midi part within the channel!!! 
This was not the case with Cubase 8 and now I have to keep going back to that in order to mix, please can a fix be created?