Something wrong with lines shading created with GL.LINES

I have to draw grid of lines as in the editor view. Also I need that grid to dissolve near the camera and on a distance. So I create a shader with SSE and apply it on lines. Everything works fine when there is some geometry in camera view. But when there no objects in scene or no objects in camera view lines become dark. What happens? And even more! In some camera position lines start blinking with about 2Hz period I use Unity 4.3.1f1, there buil-in Intel HD4000 graphics with latest driver, Windows 8. Maybe deferred rendering could help there but I have no Pro to test it.

SSE shader here:

 Shader "GridShader"
 {
     Properties 
     {
 _Color("_Color", Color) = (1,1,1,1)
 _DepthDividerExponent("_DepthDividerExponent", Float) = 10
 _DepthDividerSin("_DepthDividerSin", Float) = 10
     }
     SubShader 
     {
         Tags
         {
 "Queue"="Transparent"
 "IgnoreProjector"="False"
 "RenderType"="Transparent"
         }
 Cull Back
 ZWrite On
 ZTest LEqual
 ColorMask RGBA
 Fog{
 }
         CGPROGRAM
 #pragma surface surf BlinnPhongEditor  alpha decal:blend vertex:vert
 #pragma target 2.0
 float4 _Color;
 float _DepthDividerExponent;
 float _DepthDividerSin;
 sampler2D _CameraDepthTexture;
             struct EditorSurfaceOutput {
                 half3 Albedo;
                 half3 Normal;
                 half3 Emission;
                 half3 Gloss;
                 half Specular;
                 half Alpha;
                 half4 Custom;
             };
             inline half4 LightingBlinnPhongEditor_PrePass (EditorSurfaceOutput s, half4 light)
             {
 half3 spec = light.a * s.Gloss;
 half4 c;
 c.rgb = (s.Albedo * light.rgb + light.rgb * spec);
 c.a = s.Alpha;
 return c;
             }
             inline half4 LightingBlinnPhongEditor (EditorSurfaceOutput s, half3 lightDir, half3 viewDir, half atten)
             {
                 half3 h = normalize (lightDir + viewDir);
                 half diff = max (0, dot ( lightDir, s.Normal ));
                 float nh = max (0, dot (s.Normal, h));
                 float spec = pow (nh, s.Specular*128.0);
                 half4 res;
                 res.rgb = _LightColor0.rgb * diff;
                 res.w = spec * Luminance (_LightColor0.rgb);
                 res *= atten * 2.0;
                 return LightingBlinnPhongEditor_PrePass( s, res );
             }
             struct Input {
                 float4 screenPos;
             };
             void vert (inout appdata_full v, out Input o) {
 float4 VertexOutputMaster0_0_NoInput = float4(0,0,0,0);
 float4 VertexOutputMaster0_1_NoInput = float4(0,0,0,0);
 float4 VertexOutputMaster0_2_NoInput = float4(0,0,0,0);
 float4 VertexOutputMaster0_3_NoInput = float4(0,0,0,0);
             }
             void surf (Input IN, inout EditorSurfaceOutput o) {
                 o.Normal = float3(0.0,0.0,1.0);
                 o.Alpha = 1.0;
                 o.Albedo = 0.0;
                 o.Emission = 0.0;
                 o.Gloss = 0.0;
                 o.Specular = 0.0;
                 o.Custom = 0.0;
 float4 ScreenDepthDiff0= LinearEyeDepth (tex2Dproj(_CameraDepthTexture, UNITY_PROJ_COORD(IN.screenPos)).r) - IN.screenPos.z;
 float4 Add0=ScreenDepthDiff0 + float4( -1,-1,-1,-1 );
 float4 Abs0=abs(Add0);
 float4 Divide0=Abs0 / _DepthDividerSin.xxxx;
 float4 Sin0=sin(Divide0);
 float4 Divide2=Abs0 / _DepthDividerExponent.xxxx;
 float4 Log1=log(Abs0);
 float4 Pow0=pow(Divide2,Log1);
 float4 Divide1=Sin0 / Pow0;
 float4 Master0_1_NoInput = float4(0,0,1,1);
 float4 Master0_2_NoInput = float4(0,0,0,0);
 float4 Master0_3_NoInput = float4(0,0,0,0);
 float4 Master0_4_NoInput = float4(0,0,0,0);
 float4 Master0_7_NoInput = float4(0,0,0,0);
 float4 Master0_6_NoInput = float4(1,1,1,1);
 o.Albedo = _Color;
 o.Alpha = Divide1;
                 o.Normal = normalize(o.Normal);
             }
         ENDCG
     }
     Fallback "Diffuse"
 }