it's a bug.
they don't spout it when you enter the mission - but when you enter their area.
so if the map has multiple floors they say it when you enter the floor.
It is a very annoying bug.
I hate that, too. Patrols all seem to be triggered as soon as you enter the floor or area they are in. Hostages, etc., wait until you are within combat range, then say all of their unaware/aware dialogue at once. If you're lucky, the patrols are close enough to you that at least the $name works, otherwise that tag shows up in their dialogue instead of the players name. It is extremely annoying. I've had to cut out tags and make dialogue generic because it makes it look so stupid. 
No AV/EBs Deal with The Devil's Pawn-207266 Slash DeMento and the Stolen Weapons-100045 Meet the Demon Spawn-151099 Feedback
From what I've seen, the aware/unaware bug seems to have ended up in the regular non MA missions too.
It seems that they must have done something to adjust the radius of the triggers for each of those dialogues. Whatever they did, I hope they readjust it so it works a little more realistically.
No AV/EBs Deal with The Devil's Pawn-207266 Slash DeMento and the Stolen Weapons-100045 Meet the Demon Spawn-151099 Feedback
This has been a source of endless frustration for me. That and the fact that most battles begin immediately, so one side is usually defeated by the time the characters get there. Related I assume. I've sorta given up on fixing it, and just hope that someday the bug will be fixed, and my missions will then be a bit more coherent.
I was working on an arc that I wanted to include a batle in and the same thing kept happening to me. I've decided that I don't need no steenkin' battles. 
No AV/EBs Deal with The Devil's Pawn-207266 Slash DeMento and the Stolen Weapons-100045 Meet the Demon Spawn-151099 Feedback
So I've been trying to test my first mission, and it would appear that either:
Patrols, allies, etc all say their Unaware Dialog all at once when I enter the mission. Then they never say it again because it would appear that they are all aware of me at once... I haven't even moved. So I get the Unaware and Aware dialog coming up all at once when I first zone in.
I've tried getting rid of this by having some enemies spawn with the dialog I want triggered by other events. However, then they say nothing until I am about 2 feet from them then just spew out their Unaware AND Aware dialog all at once.
Anyone know if I'm doing something wrong? Is there a way to set their dialog to repeat every X minutes or something like that?