I recruited Jahan at the earliest possible point, and after investigating the murder scene and teleporting to the homestead, my party and I returned (a friend joined in co-op, and I initiated the teleport back) to the Cyseal north gate, and when both our companions became available to talk, I was unable to talk to Jahan.
It's been stuck as such since then, and subsequently, we got dragged into combat by me stupidly pickpocketing in the market square. We entered combat, but Jahan remained outside of combat, and could attack all the participants uninterrupted, the same way as when out of combat. He killed all the combatants unopposed and is still unable to be interacted with (but can be controlled).
Figured I'd report the bug.