Same here, I can confirm/support what the others are saying.
For me Kana reappeared in the party, but only with his starting equipment. Not sure why that was so, since I've dismissed him on multiple occasions (and for me at least his personal quest has long been completed, in Act 2, so this seems to be a problem in Act 3 only).
Edit: a (temporary) workaround is to not dismiss Kana from your party. Then all other party mechanics seem to work okay. If you already have, and you saved it, I don't think it can be helped...
I also noticed that his default Chant reappeared (March of the Kamoa), even though I'd replaced that way back at the beginning of the game.
He is also stuck in the conversation "That shade then, that was the great Od Nua?", no matter what response I give the next time the convo's the same.
Maybe this means that the game somehow tries to return him to his default state thus creating a conflict?