Buchla Thunder - Down/Up Octave affecting A & B Hex pads when note set to "Off"

I’m using the Buchla Thunder overlay with a slightly modified “Thunder MPE-CC-MIDI” Set 1 mapping.
The A and B hex pads are set to “MIDI XYZ Pad” with their note set to “Off” and they work as intended when on the default transpose position.
When transposing up or down using the Down/Up Octave MIDI Morph Modifiers, the hex pads start to send note on and off messages.
Am I missing something obvious?