I'm not sure if this is intentional or a bug, but sometimes when I approach the enemy they get an attack of opportunity on me. I'm not passing them or anything. I'll walk in a straight line right to their back and they'd attack me. Does this happen to anyone else?
Also in DOS I remember that there used to be circles that would show you the area where the enemy had attack of opportunity ability. Has this been removed because I don't see it anymore.
Seems to be a bug because in my game I still see the circles. They are red with graphical spikes.
That the enemy gets an attack of opportunity when you pass them might happen on purpose though. If you want to get in their back unnoticed you have to sneak or go invisble. But I can't say for sure, since the graphical information is missing in your case it might be buggy as well.