Anyone had success with getting bugged quests fixed?

You can no longer submit bug reports as tickets. Only report bugs on their forums, where they almost never give indication whether they've read your report or agree it's a bug. You just have to hope you see it on their Known Issues list at some point, and pray real hard it moves on to the Bug Extermination list.

Specifically for your problem: have you tried forfeiting the quest and re-accepting it? I know some boss-killing quests have a problem if you accepted them while in a party, or accepted solo but then completed when in a party.