There's spoilers below
I am 90% positive this is a glitch and there isn't something I'm missing. On the first actual mission, when you go inside the meeting room where Campbell and Curnow have their meeting, EVERYTIME that scene starts, the doors open where they are and both Campbell and Curnow just start sprinting. They don't react to me if they see me and it doesn't seem to matter if I'm hiding or not. I even triggered the scene and then left the building entirely yet they still just take off once the doors open. They will run across the entire level and then run back, repeatedly.
It doesn't seem to matter what I do, whether I keep all the doors closed, hide every single body, disable all the alarms, etc etc. They always just take off. It happened when I poisoned both glasses, poisoned just one, broke both, and left them alone. Considering I was trying to brand his ass to get the most out of my mission, I really don't want to just assassinate him, which seems to be the only option I have. Did anyone encounter this problem or am I completely missing something?
*edit* I was able to complete it without having to kill him. Campbell always seemed to run to his secret hideout room and Curnow ran... wherever the fuck he felt like apparently. I was able to cut off Campbell and knock him out and then carry his body off and escape his guards to go brand him. What a pain in the ass though and I didn't get to see how the meeting went down =(