I think I see what the bug is in the latest log - the "multichannel" mapping seems to be shared between input and output mappings:
1) Detect that output supports only 10 channels
2) Change mapping "multichannel" to 10 channels
3) Detect that input supports only 6 channels
4) Change mapping "multichannel" to 6 channels
5) Try to open output on mapping "multichannel" with 6 channels, and fail.
I think I see what the bug is in the latest log - the "multichannel" mapping seems to be shared between input and output mappings:
1) Detect that output supports only 10 channels
2) Change mapping "multichannel" to 10 channels
3) Detect that input supports only 6 channels
4) Change mapping "multichannel" to 6 channels
5) Try to open output on mapping "multichannel" with 6 channels, and fail.