Actually this happened again, when I got my block knocked off by a Hulk. It seems to happen with the flimsy/glass jaw combination. I don’t know if it’s graphical or if I actually have HP remaining. I’m going to try again and see what happens with self-aware thrown in.
Edit: It is indeed graphical. Which is good because if it wasn’t I’d be pissed. Still a bug though. Very easy to duplicate; spawn in some heavy power armor without the helmet, and spawn in a Hulk. Wait for it to put you through a wall and observe the results. Other than the hole in the wall, of course.