This issue was raised in a previous version. I can see that it is Designed to work this way, hence the feature request — it should be possible to edit MIDI during playback, while the Chord Track is set to play back through monitor-enabled channels. Currently, that’s not possible, since monitoring is automatically enabled when the MIDI editor is opened. d’oh!
Full details in this old thread… https://www.steinberg.net/forums/viewtopic.php?f=184&t=61151