If you had a character who was stage-4 before you downloaded dawnguard then he/she will still have old vanilla hostility....at least it did for me. For some reason, my dark elf vamp character who was stage-4 before i started playing dawnguard, still has the whole hostility thing, fast traveled her to whiterun and she was attacked.

HOWEVER

My high elf vamp character who was on stage-1 before dawnguard, when i started her on dawnguard and went to stage-4, no one attacked her on sight.

Has this happened to anyone else other then me? That stage-4 vamps who reached that stage before dawnguard still have vanilla hostility?

I'm sure this was not intentional but it does give me the option of being able to play a vanilla style stage-4 vamp (of course not completley since the other dawnguard changes kicked in for the character). But if this character reverts back to stage-1, then eventually gets to stage-4 like my high elf vamp did, then maybe no one will attack her.

experienced the same thing with my male high elf

Some guards aren't attacking me in Vampire Lord form, so it's not hard to believe something might have went wrong along the way.

on ocasion with a breton i started before the dawnguard by didnt get infected until the harkon offer was made.
I go to lvl 4 and people shout stuff like kill the vampire at me but they dont attack dont go hostile they just act normal but yell mean things.

My vampires cries himself to sleep of a day, then the people who called him names cry themselves to death at night.

Great news. I hope this isn't fixed. Do you know if they still attack your Dark Elf on stage 4 after you reverted back to stage one and starved yourself? Or was it fixed by feeding?

Have you tried feeding to hit stage 1 again? Try that and see what happens.

If it doesn't help, try loading the save without Dawnguard, save at stage 1, then re-add Dawnguard.

I havn't tried, but i will try to do that today to conform that.

So did it work?

this worked for people during the beta...you can also cure yourself and ask serana to turn you again and that should clear it up