Whenever a mesh is non manifold, Xmesh does add additional vertices.
This causes issues while using another caching system on top, as they rely on the vertice count.
Is it possible to turn adding additional vertices off, so it will create the same mesh like the input?
Can you send us a simple example that shows this? XMesh is supposed to get the mesh that the renderer would be handed by the original object. It is generally a TriMesh, which can handle non-manifold meshes just fine. If the mesh is converted to a Polymesh at some point on the stack and XMesh is set to save a TriMesh, some vertices would be naturally duplicated since Editable Poly in 3ds Max does not allow for some topologies like an edge shared with more then two polygons. If XMesh Saver is set to save a Polymesh, a similar behavior might occur, for the same reason. But when someone says “mesh”, I assume we are talking about the good old TriMesh format used Pre-3dsMax-R4, so additional vertices would be surprising.
So without having the source mesh, I cannot explain why you are getting additional vertices.
Hi Bobo,
The issue is related to what you described. We are moving meshes from Maya and running into this as Maya seems to be more permissive on Mesh structures. I was wondering what is we could do in order to catch these issues early on in Maya ? Is there any way XMesh could detect such pathological cases and popup incompatibility warning ?
I will have to ask the developers.
We had to do something like that in Sequoia as we needed to make sure the meshes it produced were always manifold. So I believe we do have code to test for special mesh conditions. Whether that would the right code to use is something we will have to confirm.
Can you please ensure you save one offending Maya mesh into a test file in a secure place so when the time comes, you/we can test on it?
SpeedTree trees are great exemplars.
You are assuming we have SpeedTree 
Can you get a Maya Mesh in an MB file that our developers can open and export and see the problem without installing extra plugins?
I spoke to the XMesh developer and we will look into it, but having a test case would be very helpful!
Thanks in advance!