Mirrored Normal Map Problem

In my character, the arms and legs on the right side are just the arms and legs from the left side, only mirrored.
When doing this, some problems arise.
I don't know the technical terms, but it looks like the normal map on the right limbs is being combined with the normals already on the model, where on the left (original) side the model's original normals are mostly ignored (as they should be).
Here are some pictures.

Left:


Right:


Left:


Right:


What do I do?
I don't recall ever having this problem before.

 

Anyone?

 

Normal maps are always combined with the normals that are already on the model. It looks to me like the two sides are being triangulated differently (when converting from quads to tris it's choosing the wrong diagonal).

Try trianglating the model yourself before importing to unity, so you know it's been done symmetrically?