Well, I can understand you losing it over a player trying to argue semantics against a Bluff check that was obviously well justified, and insisting on his argument that his character didn't know it was a "vampire" vs. "an undead". I'm sorry, but that's the point where a game stops being D&D and starts being Silly Buggers.
From what I get from Q's description, it sounds, to me, like the rest of the players were aware that something was going on with the dwarven character, but didn't have a clue what, and simply were reluctant to play along because they were left out of "the secret", either bored because they weren't included, or pouting. As I said, just my impression.
And from personal experience, I know how easy it is to "roleplay" your character to the last dot in its background just to annoy the DM for one reason or another, and then feign innocence, and "just playing my character's motivations". Did so myself often enough years back, wouldn't do it again, and don't think it's funny. More like childish sandlot behaviour, and not belonging in a game.Just my 2 cents.
As an addendum, I am convinced that not EVERYthing is the concern of all players all the times. A roleplaying game is not a democracy in that every player has a say in everything every time, and some things only concern the DM and another player, like a change of character. Noone can expect the others to follow a scripted path, but this wasn't the case. But you can expect them not to openly block another player "just because".