Just witnessed a very rare glitch in the forge testing arena (versus Mirrorius).
Mirrorius, armed with pontacto and metafortis (pre-activated), attacked a zombie at long-range with a bow and killed it, the log stated that an adjacent hound was also attacked and killed during the bow attack, as if it had been melee attacked..
..obviously this was impossible because the AI had already used its attack, in the form of a long-range bow shot.
Visually the hound was still intact after the bow attack on the zombie, but as the log stated, it was in fact also dead (non-selectable), it was killed at the same time as the bow shot on the zombie, probably due to some kind of rare metafortis glitch.
This glitch seems impossible to recreate in offline mode. Any bugs that existed in multiplayer relating to metafortis and bow were fixed so it might just be some strange thing that can occasionally still happen in the test arena when an AI has that particular load-out/combo.
(I took a quick video of the incident but it was terrible quality, wrong settings etc)