Non-player actor movement implementation differs from vanilla
Current implementation of AiFollow movement with toggling Run flag depending on the distance to the player seems to only suit humanoid - NPCs, didn't check bipedal creatures - followers.
In Morrowind, creature followers accelerate and decelerate gradually depending on the distance from them to the player and the time they were moving. It's somewhat subtle. In OpenMW, they run at a constant speed depending on the stance they are in. This difference makes life harder for modders who add in creature followers (got the report from one), and it seems that the movement of pack rats in Tribunal is also incorrect. Emma's wolf companion is affected.
For testing, add an AiFollow package to a rat and see what happens in vanilla and OpenMW when you move. For convenience, set its speed to a higher value in Morrowind, because it's ridiculously slow (Speed 8).