I did a search and found nothing to answer this and I don't think this belongs to the Mod The Sims.
I just got Nightlife yesterday (Yes, I'm late) and today one of my male sims became friends with the female vampire (not best friends, just friends). Then he invited her for a visit. I then got this idea to influence the vampire to bite my sim's sister. She did and I was happy... but she didn't stop there. She started to bite every other visitor too and turned them to a vampire. The ones that weren't even her friends. I didn't save because I became scared she would now start turning every sim to a vampire when she visits community lots in Downtown.
So... Is this normal behaviour or was it caused because I used that "influence" option... or is there a bug?

*EDIT*
Nevermind... When I did this whole thing normally, there seemed to be no problems. But it's still strange to me that by influencing the vampires they would do that O_o.

*EDIT again...*
Damn... It didn't work. Now that vampire is randomly biting townies while in Downtown >_<.

Grand Vampires are prone to that sort of behavior, especially when they have been influenced at some point to bite a sim. If she gets to be too much of a pain in the neck (excuse the pun) you can have someone who is friends with her buy a couple of the cure potions from the gypsy, then invite her over. Set one of the cures on the ground and influence her to drink it. (the other is in case you get bitten first.) She will still wander around with the vampire stalk, and will still say bleh a lot, but she won't bbe a true vampire anymore. The game will spawn another female grand vampire who (hopefully) will be a bit saner.

Thanks for the answer. Good to know it was actually normal. I already downloaded a hack which will stop the random biting of townies and NPCs =P. I want to be the one who decides who are going to get turned into vampires.