Will I get a fine if I "vamp-up" in front of people I kill?

In Skyrim: Dawnguard, I recently became a vampire lord (VL). Now, I know that people remain pretty peaceful if you're a vampire (and you drink regularly). However, I've read that if you transform into a VL in front of other people, you'll get a "fine" you can't pay and everyone will try to kill you forever.

Now, suppose I'm in a bandit cave and there are, say, 5 bandits. If I transform into a VL in front of them and then kill them all, will I be attacked the next time I go to town? Similarly, if I'm in town or in a populous area and I transform in front of a lone villager or two (no guards though) and kill them, will I be attacked?

This is the first I've heard of such a problem but I'll do my best to answer.

First off, yes you should be given a fine when you transform into a vampire lord, the same as if you transformed into a werewolf. It should be possible to pay it or bribe the guard if you are in the thieves guild.

Transforming inside of a bandit cave will not cause you to be attacked when you enter town next time unless you enter the town while transformed. And if you transform in front of citizens - whether or not you get away with it will all depend on how far away the nearest guard is and how fast you kill the witness. This will be difficult for transforming as they will be able to get a head start on you to reach a guard since you cannot move while transforming or for a very slight amount of time afterwards.