S4S adds weird shadow in game to exported/imported meshes

Hi. This is normal and how things work in (probably) all games. It is related to how the uvs of 3d models are converted to text information.
What you should do is just remove doubles in blender

For example, you select all body parts, then remove doubles. Then the lines along the body will not appear
Alternatively, you could remove doubles on all of the mesh, but then would get a different type of shadows along sharp edges that will need to be split. If you plan on modifying the shape of the mesh and, as a result, retransffering data, this is what you should do
It would go like this:
- in edit mode select all of the mesh with A, quandrangulate it for convenience of editing (Mesh - Faces- Tris to quads)
- Remove doubles with Merge distance set to 0,0001;
- reshape the mesh and re-transfer all the data;
- then switch shading to Solid and you will see these shadows along sharp edges. You need to Alt-click on edge loops along them and Mesh - Edges - Edge split

Hm, so i did some testing and this seems to be a problem with how this specific mesh is split into meshgroups. Why this happens and, most importantly, why this does not happen in the original is a mystery to me
1). exporting and re-importing the file into this package results in the shading problem

2). exporting and re-importing the file into a different package results in the same shading problem. So its not the package or maps
3). joining all meshgroups together and importing into a different blend fixes the problem. So its a matter of how the game shades the borders of meshgroups, not split edges

4). reshaping the meshgroup moves the problem in a different location, confirming the previous assumption

5). this does not happen with similar items