Hermod+ random note sustain issue

Hey all!
I’m loving my Hermod+ as my midi and sequencing mastermind. I’m using a Yamaha Reface CP via the USB Host port as a midi controller and sound module (you can internally un-couple the keyboard from the sound generation).

So far, so good. However, even with a blank new sequence, the notes Bb3, Eb5 and Bb5 have sustain, while all the others don’t. There is no sustain pedal connected, and no midi effects etc. set up. Any ideas where this comes from?

Edit: “Apply Sustain” in the player settings for the selected track is off.