Totally insane rendering problem- Uvs Collapsing

Hi there, I have 2 objects that I'm exporting, from maya, in FBX format. I am using a custom vertex-lit shader that I'll post below. It's very simple.

Both of those objects have 2 materials on them -- the same two materials.. Just picture one object with two materials, now duplicate that object in your mind. that's what i have.

If i export these objects by themselves, everything is fine. if i export them together, i get the following behaviour:

the objects look fine from a certain camera angle, but when i rotate the camera, it looks as though the uvs "collapse" or something - that is, the color for the materials stays correct, but there is no detail anymore, as if the uvs have been collapsed down to a point. honestly I'm not sure what's actually happening.

both objects have 1 uv channel and are mapped within their bounds. I have many other objects in the scene that have uv mapping way outside the 1,1 bound, so I'm pretty sure that isn't the problem.

oh, and by the way, this problem isn't happening with the default unity shaders.

the shader I'm using is thus:

Shader "Harmony Arcade/VertexColor Unlit" { 

Properties 
{ 
    _MainTex ("Base (RGB)", 2D) = "white" {}
}

SubShader 
{ 
   BindChannels 
   { 
        Bind "vertex", vertex 
        Bind "color", color 
        Bind "normal", normal 
   } 

   Pass{
        SetTexture[_MainTex] {
            Combine texture * primary
        }
   }

}

}

Bind "texcoord", texcoord