Combining MIDI regions

Ardour 6.9-5 on Manjaro XFCE.

Following this topic I expected that creating a new MIDI track and setting as input the output from my other MIDI tracks and hitting would combine those into the new track.

However, it turns out tracks on which I had inserted audio plugins (Calf limiter, LV2) does not output any MIDI notes to be recorded. Remove the plugin, and recording happens as expected. Is this intended behaviour?

Also, the routing grid for the combined track is confusing: in addition to the MIDI tracks, 2 of the normal audio tracks can be chosen as input (see screenshot, the 2 tracks on top are normal audio tracks while the rest are MIDI:)

I don’t have access to any of the other audio tracks (there are at least 5 more).

Anyone have an idea what is going on here?