Hi, it's my first post on the forum, welcome everybody! In the location under the Beregost there are three Flaming Fist guards, which you can fight or tell them that you are not a bandit and they let you go. The point is, that when you choose the fight option, only one guard is actually fighting, and the other two are just standing a few steps behind and doing... nothing. I noticed that it happens only if you "pull" the "I serve the flaming fist" one, out of the other's line of sight. They follow him even if you're not seeing them atm, but later they just stand in one point until you attack them directly.
EDIT: I've noticed another thing. Actually the two additional guards aren't responding to your attacks either, as long as the main guard is alive. I've blinded and then feared him, and then killed the other two without any problem.