The bell bug is still happening. It happens randomly during my solo flawless attempts. You hit the bell and nothing happens for a couple of seconds. Then teleportation and death happen simultaneously.

So the common thing is people will go into the nightmare, kill both standard bearers, but only take a single standard in order to extend the damage timer later. It causes a psion to be in the room with Ghalran's Shades. When you kill the psion it extends the damage timer. It's by far the most common way to run the encounter and it's a GLITCH. Then later on guess what else glitches? [spoiler] A bell[/spoiler] Moral of the story, every time you kill a standard bearer, grab the standard or you're asking for it to glitch out. You may even get through the encounter and have a bell glitch later in the dungeon. I can run the dungeon and make it NEVER glitch, or make it glitch nearly instantly. It's 95% player behavior and little bit of buggy programming. If you play it super straight forward, it won't glitch. You can find a lot of examples in the video I'm attaching. No funny stuff if you watch.