I've been looking back through the bug reports a bit, but have not seen this one come up:
At some point during the lever-pulling in Vurnak's Hoard (or there-abouts), character images / faces ceased being displayed along with dialogue. The text is there, but you have to basically guess who's speaking. Now I back-tracked and went the other way, thinking this may be an issue exclusive to levers. But when I hit the metal bridges over lava, it was the same thing.
My first impulse would have been to try and clear cache, but without a way to copy and save the actual game-files.. it would be rather annoying to mess things up further and perhaps be forced to start from scratch.