Account switching doesn't work correctly for drush command

Oh, super interesting! Because I tested this, and it totally worked fine and the account was switched correctly when doing a batched export.
I was surprised by this tbh, and didn't think too much about it, though I can imagine that yeah, it doesn't work in all cases!

What version of Drush are you using? Maybe that's important somehow?

The project is on Drush 13. I did find mention of a global -u option to set the user ID and the batch processing in Drush is actually trying to set it somewhere, but apparently this was removed in Drush 9, so that can hardly be a factor. Something is still off, though, since tests are failing.

I think I've sorted it by trial and error.