SetTexture In A UI Material Doesn't Update Immediately

I have a custom shader that simply masks a sprite. I have a variant of the shader to function in the UI--it has stencil buffer enabled etc. so that it can behave with masks. In game players pick the mask/shape they want their sprite to be. There's a dropdown that they select the mask out of. When they select it I call SetTexture on the UI material at that time so they can see a visual update.

It doesn't update immediately. However it does update the material accurately, it just doesn't redraw inside the UI. If I close that window and reopen it, then it draws it properly.

Any ideas on what could be causing this? Or a workaround? If it helps any here is the shader. It's the default UI shader just with the mask added in.

 // Unity built-in shader source. Copyright (c) 2016 Unity Technologies. MIT license (see license.txt)

 Shader "Custom/BallShaderUI"
 {
     Properties
     {
         [PerRendererData] _MainTex("Sprite Texture", 2D) = "white" {}
         _Mask("Mask", 2D) = "white" {}
         _Color("Tint", Color) = (1,1,1,1)

         _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
         [HideInInspector]_Cutoff("Alpha cutoff", Range(0,1)) = 0.5
         [MaterialToggle] PixelSnap("Pixel snap", Float) = 0
         [Toggle(UNITY_UI_ALPHACLIP)] _UseUIAlphaClip("Use Alpha Clip", Float) = 0
     }

     SubShader
     {
         Tags
         {
             "Queue" = "AlphaTest"
             "RenderType" = "TransparentCutout"
             "CanUseSpriteAtlas" = "True"
             "PreviewType" = "Plane"
         }

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

         Cull Off
         Lighting Off
         ZWrite Off
         ZTest[unity_GUIZTestMode]
         Blend SrcAlpha OneMinusSrcAlpha
         ColorMask[_ColorMask]

         Pass
         {
             Name "Default"
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             #pragma target 2.0

             #include "UnityCG.cginc"
             #include "UnityUI.cginc"

             #pragma multi_compile __ UNITY_UI_ALPHACLIP

             struct appdata_t
             {
                 float4 vertex   : POSITION;
                 float4 color    : COLOR;
                 float2 texcoord : TEXCOORD0;
                 UNITY_VERTEX_INPUT_INSTANCE_ID
             };

             struct v2f
             {
                 float4 vertex   : SV_POSITION;
                 fixed4 color : COLOR;
                 float2 texcoord  : TEXCOORD0;
                 float4 worldPosition : TEXCOORD1;
                 UNITY_VERTEX_OUTPUT_STEREO
             };

             fixed4 _Color;
             fixed4 _TextureSampleAdd;
             float4 _ClipRect;

             v2f vert(appdata_t IN)
             {
                 v2f OUT;
                 UNITY_SETUP_INSTANCE_ID(IN);
                 UNITY_INITIALIZE_VERTEX_OUTPUT_STEREO(OUT);
                 OUT.worldPosition = IN.vertex;
                 OUT.vertex = UnityObjectToClipPos(OUT.worldPosition);

                 OUT.texcoord = IN.texcoord;

                 OUT.color = IN.color * _Color;
                 return OUT;
             }

             sampler2D _MainTex;
             sampler2D _Mask;
             fixed4 frag(v2f IN) : SV_Target
             {
                 half4 color = (tex2D(_MainTex, IN.texcoord) + _TextureSampleAdd) * IN.color;
                 float maskRed = (tex2D(_Mask, IN.texcoord)).r;
                 color.a *= UnityGet2DClipping(IN.worldPosition.xy, _ClipRect);
                 color.a *= maskRed;
                 clip(color.a - 0.001);


                 return color;
             }
             ENDCG
         }
     }
 }