I have some new information about the North / South bug.
First and foremost, only Melee damage matters. Projectile damage is not effected. So I suppose in theory the entire bug could be negated by making all damage sources be from spells in the name of balance.
Secondly, lights. In addition to what I said in my previous post here in regards Lights on Creatures, and how a light seems to have the same offset position regardless of creature direction (as if always facing north), I found that the same is true for objects. Was tinkering around with lights for room objects, and found it to be particularly tricky to get the right settings because I quickly realized that, if I tried to offset the X / Y position of the light, it would be the same offset regardless of whether it was attached to a north, south, etc wall, as if the object was always facing north. Like it would be 0.25 tiles northwest of the object always for example, regardless of the object's apparent direction based on the model / wall it's attached to. It's the same as the creatures and, probably is a core problem with the game's handling of entities.
I am thoroughly convinced that the backstab theory is correct, just probably not the why. Objects and general entities are stuck facing north, it just doesn't look that way because it's probably data separate from the model's direction or whatever other data the game uses to get creatures moving around. So it probably went completely unnoticed as it all looks fine, like everything's rotating and all that. But this 50% damage increase only affecting melee damage makes a lot of sense with Rogues / Thieves being able to backstab. It not affecting projectiles means it probably wasn't meant to be used as a way to diversify outcome of combat.
It's also possible that this worked properly once upon a time, but something broke it later down the line and it was never noticed.