Refraction Shader Problem

Ok soo... I think my Refraction Shader that is a modified version of the unity Pro Glass Refraction Shader does something wrong here.

in the shader there are descriptions that say it will grab the screen behind that object and then it will use the normal map of this object to refract that.

but it seems it grabs also the objects infront of that plane I use in my scene here.

but I only wanted that it just bends the back of that object... is there a way to fix this?

in the pictures you see a dodecahedron and a few units behind that there is the plane with the refraction shader on it that always faces the players camera. pictures are from farthest player position to closest position.

shader code is after the pictures!

 // Per pixel bumped refraction.
 // Uses a normal map to distort the image behind, and
 // an additional texture to tint the color.
 
 Shader "TEST_Shader/Refraction" {
 Properties {
     _BumpAmt  ("Distortion", range (0,128)) = 10
     _BumpMap ("Normalmap", 2D) = "bump" {}
 }
 
 Category {
 
     // We must be transparent, so other objects are drawn before this one.
     Tags { "Queue"="Transparent" "IgnoreProjector"="True" "ForceNoShadowCasting"="True" "RenderType"="Transparent" }
 
     SubShader {
         Fog { Mode Off }
 
         // This pass grabs the screen behind the object into a texture.
         // We can access the result in the next pass as _GrabTexture
         GrabPass
         {
             Name "BASE"
             Tags { "LightMode" = "Always" }
          }
          
          // Main pass: Take the texture grabbed above and use the bumpmap to perturb it
          // on to the screen
         Pass
         {
             Name "BASE"
             Tags { "LightMode" = "Always" }
             
 CGPROGRAM
 #pragma vertex vert
 #pragma fragment frag
 #pragma fragmentoption ARB_precision_hint_fastest
 #include "UnityCG.cginc"
 
 struct appdata_t {
     float4 vertex : POSITION;
     float2 texcoord: TEXCOORD0;
 };
 
 struct v2f {
     float4 vertex : POSITION;
     float4 uvgrab : TEXCOORD0;
     float2 uvbump : TEXCOORD1;
 };
 
 float _BumpAmt;
 float4 _BumpMap_ST;
 
 v2f vert (appdata_t v)
 {
     v2f o;
     o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
     #if UNITY_UV_STARTS_AT_TOP
     float scale = -1.0;
     #else
     float scale = 1.0;
     #endif
     o.uvgrab.xy = (float2(o.vertex.x, o.vertex.y*scale) + o.vertex.w) * 0.5;
     o.uvgrab.zw = o.vertex.zw;
     o.uvbump = TRANSFORM_TEX( v.texcoord, _BumpMap );
     return o;
 }
 
 sampler2D _GrabTexture;
 float4 _GrabTexture_TexelSize;
 sampler2D _BumpMap;
 
 half4 frag( v2f i ) : COLOR
 {
     // calculate perturbed coordinates
     half2 bump = UnpackNormal(tex2D( _BumpMap, i.uvbump )).rg; // we could optimize this by just reading the x & y without reconstructing the Z
     float2 offset = bump * _BumpAmt * _GrabTexture_TexelSize.xy;
     i.uvgrab.xy = offset * i.uvgrab.z + i.uvgrab.xy;
     
     half4 col = tex2Dproj( _GrabTexture, UNITY_PROJ_COORD(i.uvgrab));
     return col;
 }
 ENDCG
         }
     }
 
     // ------------------------------------------------------------------
     // Fallback for older cards and Unity non-Pro
     
     SubShader {
         Blend DstColor Zero
         Pass {
             Name "BASE"
             SetTexture [_MainTex] {    combine texture }
         }
     }
 }
 
 }