I joined the Dark Brotherhood and noticed something strange while doing assassination missions. When I have an quest active to kill so-and-so, they do not respond to the world around them. As an example, I had to kill a guy and I was next to him and invisible. Then a dragon came around and started attacking me. The target did not react to the dragon being there at all. To make matters worse, he didn't seem to even take any damage from it.

I attempted to have the dragon kill the guy for me by drinking a fire res potion, then position the guy between me and the dragon. The dude just stood there like nothing was going on when the dragon breathed fire on him to get to me.

Is this normal or maybe some bug due to the quest?

Can you talk to the target?

Try loading a save from before you got this quest and try it again. Especially if this is one of the Radiant Quests that they send you out on. Always save before you get one of those quests, no matter what faction gives it to you.

That's what he gets for enchanting, fire resistance.

Never had something like this happening to me, though.

thats weird.

I was doing a quest for the thieves guild to change a ledger at the windhelm stables. A dragon came by and killed the stable master. Yet I failed for killing my mark?