Thrawn said to post this here, as he wasn't sure himself if it was a bug:

I was in the arena, peacefully summoning stuff with my bugged silverfin skeleton reagent, when a magic eater appeared. The arena is warded.

Pointing this out, as I would like to know if it's normal or a bug.

This is a bug, sounds like the area wasn't properly tagged with the appropriate variable.

Fixed.