Hi Matthias
My cubase connections are in Stereo output pairs as I tend to use stereo group outs for monitoring to my desk
RME Totalmix FX inputs are Mono in
RME Totalmix FX Outputs are Stereo
Cubase 8.05 running on Windows 8.1. All drivers for everything are up-to-date.
To reproduce the issue here what I've found
Set up a track in cubase routed to a stereo out routed to say Outputs 17+18
Select the input as Mono input 1 in cubase for the audio track and monitor the input
Watch the matrix. Track 1 is routed to 17+18 correctly
Now without turning off the monitoring in Cubase change the input to 2 on the audio channel
Look at the matrix.... input 1 is still left routed to 17+18 as is Input 2!!!
Interestingly - Change the input to 3 and now inputs 1, 2 and 3 are left sent to 17+18
Now... change the input back to 1 on the channel and I've just noticed that all the assignments above go away and I'm left correctly with input 1 sent to 17+18 as desired.
Is this clear?