I used an invisibility potion on Lantry during a fight with some Vendrien Guard. Several hours later, I eventually realised that Lantry was still sporting a 'transparent' effect. Not only that, but enemies won't target him. Hell, I can use the guy to single-handedly block choke-points and watch as enemies scramble about helplessly. Encounters have now become trivial and I'm too far in to restart.

Has anyone else encountered this problem and, if so, is there a way to "dispel" it?

The effect is still active after resting. Also, I forgot to add, Lantry refuses to change stances. Thank goodness for autosaves.