Decided to level my performer despite past frustration, because they do make very good defenders, and figured out how to manage them effectively. I didn’t do an exhaustive test, but I do know which actions triggered the bug.
- Hitting with any harvesting tool. Make sure they move clear before you hack at things on the ground.
- A power attack with the shield. Landing a shieldsmash with a mace didn’t trigger it, but knocking them into the air with the shieldsmite did.
When I avoided doing those, I had a long and productive expedition with my performer. There may be other things that trigger it, habits that you take for granted because they don’t appear to affect other followers.