Well, yes and no... the guy was trying to do pretty much the same thing, and people talk about having issues with duplicating with or without freezing transform, but to be honest, I must have tried every combination of freezing / not freezing. I always got the same shading errors on the duplicated object.
Actually, having checked the normal directions in Maya after the duplication, Face AND Vertex normals are the same for the duplicated object right after duplication, so the normals cannot be the problem. I expect the same to hold true for duplicating within unity, as the end result looks the same.
What else could lead to this shading error?
EDIT:
To be correct, the mesh shading of the duplicated object in Maya IS black without two sided shading, so it looks like the faces are flipped, even though the normals look to be the right way up. Reversing the normals does not flip the shading... What the hell?
Anyone can make any sense of that?
EDIT2:
After some more trying: I was able to flip the normals so that the shading looked correct in Maya (must have locked something before). Now I get everything shaded inside out in Unity. WTF?
It looks like the shading in Maya LT is completly bugged for stuff that gets negative scaling, its the wrong way round. On the other hand, just looking at the normals, I cannot get the mesh to show up correctly in Unity, no matter what I do to the normals. Even if the Face and Vertex normals are correct, shading is off as shown before in the pictures.
Any possibility to duplicate the meshes in 3D Coat already so I don't need to find crippled ways of doing this rather simple task in even bigname 3D Packages?
EDIT3:
Yes, I found a way to achieve what I want without shading errors... though it is EXTREMLY unelegant. I cannot believe there is no other way to achieve a simple symmetrical mirror without shading problems in Maya LT in 2015!
Anyway, rant mode off.
What I will do now is mirror everything with the "mirror geometry" tool, separate the mesh, and export the mirrored part into its own fbx file... after cleaning up the pivot and centering it, I should be ready for final assembly. I will have to place it at the right spot manually, which shouldn't be too hard now that the object is correctly centered.
Gonna go vent some steam somewhere now... whew, that was like a thousand times harder than expected
if somebody has a better way of achieving this, I would love to hear it!
Gian-Reto's post in Blender misbehaving: good free / low cost alternative to change pivot / duplicate mesh? was marked as the answer