OK sorry re delay got caught up on some re-recording over the weekend!!
 
Just tried Thorn v1.01 - double midi recording as reported.
Updated to v1.03 and all now seems OK
Hope this helps
Nigel
 

Thorn has just been updated to 1.0.4. Dmitry has resolved the issue of recording duplicate notes when "Enable MIDI Output" is checked by adding an option to Thorn to disable MIDI output. There are other changes in 1.0.4 also, including adjusting the polyphony method to try to prevent sustained notes from being stopped.

Thanks Mitch, I will update the title of the OP