Hidden opponents

I didn't notice this until the most recent build, but it's possible that it's been there and I just wasn't fighting stealthy people until now. Has anyone run into a problem where stealthy people aren't actually stealthy?

My party will be walking through a room, and I'll see several men of dubious disposition -- call them "thugs" -- walking toward me at a slow, zombielike pace. Given that they're red, I attempt to cultivate in them a renewed awareness of their own mortality through whoopass, but although I can see them and have a clear path to them, I cannot actually select them as combat targets. I have to wait until the slow-moving stealth guys sneak attack me and come out of hiding to administer my paladinic brand of justice.

(Or, you know, drop a fireball in the area. That works too.)

It's not a killer, but inasmuch as I HAVE a suspension of disbelief, this breaks it. "Uh, guys. You know I can see you, right? I'm not one of those tyrannosaurs from Jurassic Park. I can see you even if you're standing still. Guys? (sigh) Okay, sorceress, fireball away."

"I attempt to cultivate in them a renewed awareness of their own mortality through whoopass"

Lol, yes I can only guess your in the house trying to stop Moria kill the informant (good) or assassinate the informant (evil).

At first I wondered if it had something to do with the difficulty settings but I don't think so, but it could also be we had high enough ability to see through their Stealth(?).
Or it’s just a weird bug that somehow got passed Q&A, since afaik everyone has this problem/bug.

I've had the stealth work a few times--i.e., pop into a room abruptly and NOT see the opponents til the sneak attack, but in most of the Informant quest, I could see them coming. However, iiirc, I could also target them most of the time. I'm playing on the last patch but one.