Help needed - MIDI Learn Feature for On/Off-Switches Creates an Error

Hi,
I have midified an old analog organ and now try to configure Organteq 2 (version 2.1.2 on  LINUX):

I try to MIDI learn a controller on channel 4 controller 40 (righ click on Coupler, assign MIDI). It is a 2-position switch which sends value 127 for on and 0 for off. The on event is processed just fine, however when I switch to off I get this error:

Midi Learn failed to assign Controller 40 / Channel 4 to Coupler Switch 3, please make sure to move the same controller twice, first on then off.

This is the same for all controllers I try to teach. I can confirm in the Midi mappings window that no other messages are sent in between. Manually assigning the controller to the coupler works flawlessly.

I'd like to show my customer how to retrain stop switches, therefore it would be nice to get this working, any hints are welcome. I could alter what the controller sends if that should be something else.
Thank you!
Peter