Yes. It appears Flatten only modifies the active version. BUT. It's complicated.
It appears also that the Arranger track has versions, even though it's not documented and, doesn't have a TrackVersions tab in the inspector.
try this repro:
- New project, Arranger Track, Midi Track
- select Midi track, create new version
- select both the Arrange track and midi track
- switch to the other version
Cubase will say "This track version does not exist on these selected tracks: -Arranger Track".
- Use either of the options, Duplicate or New Empty, it will to add a version to the arranger track, but of course there is no where to see this.
-- You can test it though, by adding an event to the arranger track and invoking "Previous Track Version" and "Next Track version" with only the Arranger track selected.
Switching between and adding versions appears to work; but Cubase eventually quits unexpectedly after this activity continues for a short time.