Problem with shadow casting on transparent material

Here's code of a shader below that makes material accept shadows on invisible objects. It works quite well with Directional Light for me. But when it comes up to use this one with Point or Spot light types (switching to Deferred Lighting rendering path) it doesn't work. So what's wrong with it? Is there any solution?

     Shader "Transptest"
     {
             Properties
             {
     _MainTex("MainTex", 2D) = "black" {}
     _Cutoff("Cutoff", Range (0, 1))= 0.5
     _MainColor("_MainColor", Color) = (1,1,1,1)
      
             }
            
             SubShader
             {
             Pass {
                     Name "Caster"
                     Tags { "LightMode" = "ShadowCaster"  }
                     Offset 1, 1
                    
                     Fog {Mode Off}
                     ZWrite On
                     ZTest LEqual
                     Cull Off
                     Alphatest Greater [_Cutoff]
      
     CGPROGRAM
     #pragma vertex vert
     #pragma fragment frag addshadow
     #pragma multi_compile_shadowcaster
     #pragma fragmentoption ARB_precision_hint_fastest
     #include "UnityCG.cginc"
      
     struct v2f {
             V2F_SHADOW_CASTER;
             float2  uv : TEXCOORD1;
     };
      
     uniform float4 _MainTex_ST;
      
     v2f vert( appdata_base v )
     {
             v2f o;
             TRANSFER_SHADOW_CASTER(o)
             o.uv = TRANSFORM_TEX(v.texcoord, _MainTex);
             return o;
     }
      
     uniform sampler2D _MainTex;
     uniform fixed _Cutoff;
     uniform fixed4 _MainColor;
      
     float4 frag( v2f i ) : COLOR
     {
             fixed4 texcol = tex2D( _MainTex, i.uv );
             clip( texcol.a*_MainColor.a - _Cutoff );
            
             SHADOW_CASTER_FRAGMENT(i)
     }
     ENDCG
      
             }
            
            
                     Tags
                     {
     "Queue"="Geometry+500"
     "IgnoreProjector"="False"
     "RenderType"="Transparent"
      
                     }
      
                    
     Cull Off
     ZWrite On
     ZTest LEqual
     ColorMask RGBA
     Alphatest Greater [_Cutoff]
     Fog{
     }
      
      
                     CGPROGRAM
     #pragma surface surf BlinnPhongEditor  vertex:vert
     #pragma target 2.0
      
      
     sampler2D _MainTex;
      
                             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 {
                                     float2 uv_MainTex;
      
                             };
      
                             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 Tex2D0=tex2D(_MainTex,(IN.uv_MainTex.xyxy).xy);
     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 = Tex2D0;
     o.Alpha = Tex2D0.aaaa;
      
                                     o.Normal = normalize(o.Normal);
                             }
                     ENDCG
      
             }
            
      
             Fallback "Diffuse"
     }