volca drum single channel mode - polyphony - bug?

[andete]

Hello,

I'm controlling my volca drum (latest 1.14fw) from a keystep pro. It requires using the single channel mode.
This works mostly fine, except when playing two different sounds at the same time. This works sometimes, but in this example sometimes the kick is not played by the volca drum.

I always see the following midi sequence, which seems fine, having a note-on and note-off as expected.
What I'm doing here is starting the transport, playing the first and 3rd note at the same time, and then stopping the transport again.

FA
99 3C 64 | note-on
99 40 64 | note-on
91 1A 64
F0 7F 7F 06 02 F7
81 1A 00
89 40 00 | note-off
89 3C 00 | note-off
91 1A 64
81 1A 00
FC

When I try the same with the sequencer build into the volca drum it always works fine.
I wonder if I misconfigured the volca drum somehow?
I tried turning on and off "MIDI RX ShortMessage" but it doesn't make any difference. I also tried switching back to midi channel 1 from 10 and it didn't make any difference either.