I followed up on github as you suggested and a very nice young man took a look at it and said that the code already does work the right way (at least the way I and their little poll think it should work). But, it turns out that the fix (from 2021) has not been deployed - it’s to be in the next release.
So I don’t know what will happen now - I’ll continue to use my workaround, so I’m happy enough.