For ages I have dreaded trying to get the skill point quest in Volenfell completed. If someone is on the quest, and others aren't, hitting the pair of levers just after the second to last boss is flaky - if someone on the quest hits them, it works out okay, but if someone not on the quest beats them to it, the quest will not progress. The last two times I have tried this has happened to me, and I know it has happened in the past.
If you have the quest and someone without it uses the levers, the quest will not progress past "Find the Release Lever in the Guardian's Skull." I can only hope this is unintended behavior and that it can be corrected, because I can't stress how annoying it is to make it to nearly the end just to have the quest screwed up and have to re-run the dungeon and hope to be faster.
Note that defeating the last bosses does not cause the quest to flip over to completed, which would probably be the easiest fix. Also, despite being in 4 active guilds, there is not always someone available to assist. It's getting to the point where I'm willing to take the slow boat and just solo it, though being on under 50 characters it would take a while. And this might not be an option for everyone, especially no or low CP or impaired gameplay capability. I'd much rather see the problem resolved for everyone.