For some reason that I don’t know when you bake a tangent normal map Blender have the UV island position/rotation in the reference to make the bake.
Obviusly you never could have a UVs with all correct in that aspect. I don’t know if we have some way to avoid this inside blender. We have a node for cycles to use this normal map properly, but if you want the normal map for a game engine…
Nothing special, you only need triangulate the mesh before export. If you make the bake out of Blender you will need triangulate the mesh for the process also.