Aim offset causes one bone to offset (randomly?)

Hello all,

I am having a problem with my new character rig. I have an Aim Offset asset for the pitching and several anim sequences like the idle or the sprint anim for it.
Here is how they look in the editor:

(Aim Offset)
link text

(Idle sequence)
link text

And here is how they look like when the Aim Offset is applied to a sequence (Using the “Preview Base Pose” property of the Aim Offset asset):
link text

The issue is that no matter which anim I apply the Aim Offset to, it will always offset the hips bone’s transforms kind of randomly, even though it’s location is neither animated in the Aim Offset’s animations nor in the sequence I tested this.

So why is this happening?
Is it a bug or is there a problem with the skeleton?