UI with no Ztest appearing behind geometry when masked.

So I have a world space canvas for a HUD which has a load of UI with a no ztest shader.
All of the UI works and appears in front of all geometry unless I mask it.

I did have to follow the following to get the mask to work (clearMask gameobject in the screenshots below), as im in deferred rendering: http://forum.unity3d.com/threads/ugui-masking-blocked-by-background-meshes.270122/

Here’s my hierarchy:

Here in the bottom left corner you can see the masked element being drawn behind geometry:

Here’s the UI shader im using (applied to the HUDUI material):
Shader “UI/Default_OverlayNoZTest”
_Color (“Main Color”, Color) = (1,1,1,1)
_MainTex (“Alpha (A)”, 2D) = “white” {}

		_StencilComp ("Stencil Comparison", Float) = 8
		_Stencil ("Stencil ID", Float) = 0
		_StencilOp ("Stencil Operation", Float) = 0
		_StencilWriteMask ("Stencil Write Mask", Float) = 255
		_StencilReadMask ("Stencil Read Mask", Float) = 255

		_ColorMask ("Color Mask", Float) = 15
		_Illum ("Illumin (A)", 2D) = "white" {}

		LOD 200

			"Queue" = "Transparent"
			"IgnoreProjector" = "True"
			"RenderType" = "Transparent"
			"LightMode" = "Vertex"

			Ref [_Stencil]
			Comp [_StencilComp]
			Pass [_StencilOp] 
			ReadMask [_StencilReadMask]
			WriteMask [_StencilWriteMask]

		Cull Off
		Lighting On
		ZWrite Off
		ZTest Off
		Offset -1, -1
		Blend SrcAlpha OneMinusSrcAlpha
		ColorMask [_ColorMask]

				#pragma vertex vert
				#pragma fragment frag
				#include "UnityCG.cginc"

				struct appdata_t
					float4 vertex : POSITION;
					half4 color : COLOR;
					float2 texcoord : TEXCOORD0;

				struct v2f
					float4 vertex : POSITION;
					half4 color : COLOR;
					float2 texcoord : TEXCOORD0;
					float2 uvIllum : TEXCOORD1;

				sampler2D _MainTex;
				float4 _MainTex_ST;
				fixed4 _Color;
				float4 _Illum_ST;

				v2f vert (appdata_t v)
					v2f o;
					o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
					o.texcoord = TRANSFORM_TEX(v.texcoord, _MainTex);
					o.color = v.color;
					o.uvIllum = TRANSFORM_TEX(v.texcoord, _Illum);
					o.vertex.xy += (_ScreenParams.zw-1.0)*float2(-1,1);
					return o;

				half4 frag (v2f i) : COLOR
					half4 col = i.color;
					col.a *= tex2D(_MainTex, i.texcoord).a;
					col = col * _Color;
					clip (col.a - 0.01);
					return col;


Just in case someone else encountered this, use the custom shader on the masking graphics too.
I guess that if the mask tests the zbuffer first, it won’t never draw the “stencil hole” to display the text inside, so both need to use the customized shader