Knocking a monster into lava triggering impossible warnig "deleting
worn object" for a wooden shield. The monster had to be wearning
flammable armor and be fire resistant to survive instead dying and
dropping inventory, and it couldn't be a creature that can survive at
lava locations like a salamander and the armor needed to already be
thoroughly burnt.
It wasn't hard to figure out what needed to be fixed, but it was very
hard to reproduce the situation in order to verify that fix. The
report was for monster vs monster knockback but I jousted with a lance
instead. I still don't understand why burning up a worn wooden shield
triggered the warning but burning up a worn orcish cloak did not.