For whatever reason, humanoid characters in Oblivion seem to remain stationary in combat. I noticed that my CM Partners companions halted in their tracks the second combat began suddenly and have continued doing so for some time since; one is an archer and she fires from her position, but she nevertheless refuses to budge, and bandits exhibit the same vexing behavior pattern. Monsters, however, appear to be behaving relatively normally.

Any thoughts as to what could be causing this?

Upon further testing, it evidently happens to creatures as well and is particularly prevalent in outdoor areas. They'll use long-range attacks, but they adamantly refuse to budge once combat has been initiated. For what it's worth, I have the following installed:

CM Partners
CM Partners Special NPCs
Natural Environments
Amaterasu no Yume
Oscuro's Oblivion Overhaul
Slof's Clouded Leopard Race
Lineage II Elves
DMC Stylish
Silver Ranger - Animation Replacer
Blackmarsh Hall
Tears of the Fiend
Ruined Tail's Tale
Vilja Companion Mod
Alternative Start
Actors in Emotions
Chase Camera Mod
Clamshell Cottage
Daggerfall Memories: Cybiades
Scarves!
Status Bars
Animated Window Lighting System
Custom Race Fix

Yeah, so, uh... I'm really at a loss here. I'm not entirely sure how this even began, as I haven't installed anything new.

Aha, think I resolved it. Vilja seemed to be the problem. Catastrophe averted, but it's a pity I have to uninstall such a great mod.