Thanks for the example. In this case, the FX is outputting only one note-on event, and no note-offs. You can see this by inserting ReaControlMIDI or JS/MIDI/midi_logger after the JS FX. [edit] With the FX parameter set to 1.0, the FX outputs one note-on, then 448 ticks later a note-off, note-on, and note-off all at the same time: So, the FX output is getting recorded properly -- in this case the problem is with the FX.