I'm not sure if this was reported before, or if it was already fixed (Sorry if so), but there was a bug that I noticed when using version r6640 (and I tested this with r6694 and it still exist).
I've noticed that when playing on easier skill levels (like piece of cake, or skill 0 which have no enemies or items) useractor enemies that have lotags for only apeearing on lets rock, etc. still appear despite i'm not playing on lets rock, or above. But however, they are fully brighten up, even when in dark environments, and they won't move at all, like as if they were statues. Also they cannot be killed either (But they can turn if you hit them). This doesn't happen with the vanilla Duke 3D enemies as far as I know.
Here are some pictures of the bug in action, playing on my map, Dawn of the Pork.
And here are the tags for them in Mapster32.
EDIT: Apparently this can also happen to Protector Drones as well, but weirdly it only happens when playing with mods, it doesn't happen when playing Eduke32 with vanilla Duke 3D. Did I broke something?
EDIT2: Nevemind I'm such a idiot. I did something in EVENT_SPAWN that caused this bug. Should've studied this more, but I don't think straight. I can fix this. I'm sorry for the trouble.