Vertices behaving like parented bone is rotating when neighbouring bones rotate e.g. When I rotate the character's upper shin bone, the vertices behave as if her lower thigh bone is also rotating.


The vertices around the lower thigh are not weighted to anything else but the thigh bones and I only have one armature modifier. I'm fairly certain it's reacting to that unmoving lower thigh bone but just don't know why.
I don't even know what to google for this problem!


I have used many many bone constraints on this rig but as far as I can tell no constraint should result in a mesh deformation without the bone actually moving.
Does Blender just become glitchy when you use too many bone constraints? 

[edit] I also want to add that this problem is absent when I import the model and animation into Unreal Engine 4 so it's looking more and more like a bug or a Blender feature that I'm not aware of.
Okay so I fixed it, I think. I just dissolved the lower thigh bone and subdivided the upper one and gave the new one the same name as the old lower thigh bone so the weights would sync up.

I still have no idea what the problem was but it's gone now.