Problem with External Instr. - mono/stereo issue

hello all,

i am trying to set up my hardware synth (Kurzweil K25) as an External Instrument in Cubase. The problem i’m facing is that although i set up 2 stereo return buses one of them comes in as mono. This is not a problem of my audio interface, i can see that both stereo pairs from the synth are coming in as stereo and i have set up the correct routing for the returns in Cubase.

I’ve tried this numerous times starting from scratch, with different channels, settings, creating the midi device from scratch, using a preset midi device, restarting … etc

am completely stuck, have searched the manuals and read all relevant docs … could this be a bug ? :confused:
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If you try to delete all your External Instruments, and create MIDI track and Stereo Audio track, how does it look? Is the signal mono or stereo? Are you sure, you don’t use any of this bus for different routing (bus)?