Re-reading the manual, it appears the intention is for the dry signal to remain separated (see below).
That would indicate that ModEchoVerb is the true bug with Input 1 Dry going to Output 2.
The remaining ones would be a new feature request to have a dual-mono mode for the A/B setup above, with priority given to the ones listed in section #2.
From the manual:
The H9 detects which input and output jacks have cables plugged in and routes
audio I/O accordingly. With a Mono Input (Input 1) and Stereo Outputs, the dry
contribution for both outputs comes from the Mono Input (Input 1). With Stereo
Inputs, the dry contribution at Output 1 is from Input 1 and the dry contribution
at Output 2 is from Input 2, thereby maintaining the original signal stereo image.
