Vertex transforms in custom shader don't work in Unity 5

I have vertex shader where I transform vertex positions like this:

 Input vert(appdata_full a)
    {
     Input o;
 
     float4 v = a.vertex;
 
     float4 vPos = mul (UNITY_MATRIX_MV, v);
 
     vPos += float4(xOffset, 0, 0, 0) * (vPos.z * vPos.z * someCoef);
     vPos = mul(UNITY_MATRIX_P, vPos);
 
     o.pos = vPos;
     return o;
    }

Code is pretty obvious, the further object from camera more vertex transformed.

It was working OK without any troubles. In Unity 5 it works only in Editor. When I deploy my project on device it seems like there is no vertex transformations at all! May be someone knows what the difference between new unity and unity 4 that causes this behaviour.