Has this ever happened to you in MudBox, that parts of the geometry (their UVs) are on different sides when doing a "Flatten to UV Space"?
The most common reason is that you have these polygons normals reversed, but if the normals of your geometry are correctly oriented, go to "UV Editor" and click on the "Toggle Shaded UV Display" button
There you have, Red UVs or Flipped, a real headache if you had never seen them (I say from experience) and you dont know why you still give that failure in Mudbox despite your normal are perfectly (more than failure is a nuisance when it comes to texturizing)
This usually happens when we work modeling in symmetry, Having created an X-1 Instance (Y or Z, as the case) of our half geometry
But we easily fix them this way:
So since I knew this detail, in my geometries I always have a look at both things (normals and Uvs) before exporting it to the next step of Workflow