Mesh deformation is causing the mesh to tear.

I am currently working on an application that has to reshape a mesh. Specifically I am trying to make the top portion of the mesh form itself to another mesh and take it’s shape. The problem I am having is that when I perform the deformation the top part of the mesh that is being deformed completely separates from the bottom part. What’s more interesting is that when I export the resultant mesh it seems that Unity is creating new vertices as the vert count goes from about 6400 on the original mesh to 7200 on the deformed mesh. Does anyone have any idea what might be going on here?

Thanks.

Edit:

Upon further investigation it looks like Unity is adding duplicate vertices when the .obj mesh file is imported. In my example I created a simple mesh with 62 vertices and when it gets into Unity there are 94 vertices then when I try to deform it it comes apart. The place that it tears is where the mesh is at a ~90 degree angle to itself so does Unity duplicate vertices between faces where the normals are steep, possibly for smoothing?

Edit #2:
Apparently Importing it as an FBX file is worse, it’s up to 110 verts when I load it that way.

Just checking – often the mesh already has holes in it, like T-intersections. They’re size-0, but when you deform, they open up.

For the vert count, are the before/after both the ones reported by Unity? I think Unity always reports the real count, so shouldn’t change on any deform (whereas many 3D applications count split verts as just one.) If so, seems like the deform must be adding verts (like for smoothing or something?)