Okay, I started Dawnguard and went to the first dungeon. I stealthily killled the first enimies, but they never became alert when I fired my crossbow. I thought that it was just a small glitch, until I ran into a vampire and she said "Don't talk to me meat." Then she stood there staring at me like I was the idiot. So I walked away, killed a few skeletons, met another vampire and she said "Yes?" So, again, I walked away. When I reached the boss, he attacked me along with his thralls...while his vampire friends just watched. I thought the dungeon was glitched, but every single non-boss vampire I've met afterward has just stood there and stared at me. I'm still trying to decide if this is a blessing or a curse. Or maybe the vampires decided to take a passive agressive stance to this war and I'll recieve a strongly worded letter very soon from Harkon and his court. Anyone else have this problem.

This has happened to me with 'friendly Forsworn', so I can believe it has happened with vampires too.

Yeah, same thing happend when I was walking to Whiterun,

Never happened to me yet. Everythign attacked me the first dungeon I went through.

Yeah, I'm on my fourth playthrough of the DG quest line and have experience this on my newest character. With the last three playthroughs everything was normal and now all of a sudden they don't see me as a threat and I can just hit them with arrows or crossbows until they're dead and they couldn't care less.

Lol that must have made the mission pretty simple to do then. Try reloading a clean save, if that doesn't work, try rebooting your console/pc. If your on pc you could use console commands to make them aggressive.

NNnooooo Not a strongly worded letter!! Perhaps they will send you a Cease and Dissist Hostilities Legal letter instead, try to take you to Vampire Court for damages to live stock and skeletal servants wrongful second-death lawsuits.

Never had this problem. I was curious why these random vampires in the wild were attacking me and Serana even though i'm currently a vampire.. Possibly its political manevuring of lesser vampires, trying to take out the boss's daughter... Damn Vampires..I'm so going back to being a werewolf as soon as I max the vampire perk tree.

I figured it out. It seems that the Voice of the Sky blessing you get from going to High Hrothgar and clicking all 10 stone tablets (Which is supposed to make animals neither attack nor flee from you.) has the added effect of making vampires ignore you unless hit with a melee weapon. I can hit them with a crossbow or a bow while standing right in front of them and they will do nothing, but when hit with a melee weapon they will attack as normal. Once the blessing is gone they will attack you as they normally would without the blessing.

If you are playing on pc and you have used mods on the save game that may have something to do with it. Some mods will break the "attack on sight" line of coding and may even make citizens attack you as if they were bandits. This can and most of the time will continue after uninstalling the problematic mod and can sometimes be caused by uninstalling mods.