Thanks for any assistance you can provide on this. I've been iterating on this for a while now and am somewhat flummoxed by the problem.
I have a small .blend file here which illustrates the problem:
This object (a scroll and pegbox for a violin model) is enclosed and has no non-manifold geometry or duplicate vertices.
On the bottom front right of the mesh, you see that the mesh tapers down. On the bottom left, I've moved two vertices out slightly to demonstrate the problem.
When the bottom part of the model is shaped like this on both sides (as it is on the right side of the mesh in the .blend file):
Everything works fine.
If, on the other hand, the model is modified like so:
Then recalculating normals does not work properly. Blender flips normals improperly.
You can see this for yourself by opening the .blend file I posted above, pressing A and CTRL-N. If you move the edges back so they are not in front of the rest of the model, it works correctly.
My question is: Is there something wrong with this mesh to make it do this? Or is there a bug in Blender? I'm concerned that there's a problem in my mesh that makes it hard to determine the inside and outside, so I'd like to resolve it if there is.
I'm using Blender 2.73 on Windows 8.
Thank you for any assistance you can provide!
Edit: I don't feel this is a duplicate, based on the question linked. I've provided a specific example that demonstrates a reproducible scenario of incorrectly calculated norrmals.