WebCamTexture with custom VertexShader?

On Android if I use a WebCamTexture with a custom vertex shader my Acer tablet is rotating the texture 90deg different from when running on a Android phone.

What is Unity doing in there vertex shader i'm not?

 Shader "PurplePenguin/CameraShader"
 {
     Properties
     {
         _MainTex ("Base (RGB)", 2D) = "white" {}
         _Rotation ("Rotation", Float) = 0
         _FlipX ("FlipX", Float) = 0
         _FlipY ("FlipY", Float) = 0
         _TextureWidth ("TextureWidth", Float) = 1
         _TextureHeight ("TextureHeight", Float) = 1
     }
     
     CGINCLUDE
     #include "UnityCG.cginc"
     
     struct v2f
     {
         float4 pos : POSITION;
         float2 uv : TEXCOORD0;
     };
     
     sampler2D _MainTex;
     float _Rotation;
     float _FlipX, _FlipY, _TextureWidth, _TextureHeight;
     
     v2f vert( appdata_img v )
     {
         v2f o;
         o.pos = mul(UNITY_MATRIX_MVP, v.vertex);
         
         // Image Rotation
         float2 xVec = float2(cos(_Rotation), sin(_Rotation));
         float2x2 mat =
         {
             xVec,
             {-xVec.y, xVec.x}
         };
         float2 uv = v.texcoord - .5;
         uv = mul(uv, mat) + .5;
         
         // flip uv over the y or x
         float xUV = (_FlipX == 0.0) ? uv.x : (1.0-uv.x);
         float yUV = (_FlipY == 0.0) ? uv.y : (1.0-uv.y);
         uv = float2(xUV, yUV);
         
         uv.x *= _TextureWidth;
         uv.y *= _TextureHeight;
         
         o.uv = uv;
         
         return o;
     }
     
     half4 frag(v2f i) : COLOR
     {
         /*half4 color = tex2D(_MainTex, i.uv);
         
         // invert color
         half temp = color.r;
         color.r = color.b;
         color.b = temp;
         
         return color;*/
         
         return tex2D(_MainTex, i.uv);
     }
     ENDCG
     
     SubShader
     {
          Pass
          {
               //ZTest Off
               //ZWrite Off  
 
               CGPROGRAM
               #pragma fragmentoption ARB_precision_hint_fastest
               #pragma vertex vert
               #pragma fragment frag
               ENDCG
           }
     }
     Fallback off
 }