SkyBox doesn't clear with Greater ZTest effect

Hello,

I'm trying to do a bit of at trick to get silhouette reflections on arbitrary shaped mesh (for the ocean shader project)

inspired by this tutorial:
http://www.burgzergarcade.com/tutorials/game-engines/unity3d/unity-ios-shaderlab-tutorial-9-ztest

The strategy is to render a reflection pass with all the objects flipped and only showing the bits that are underneath the water, which will create a nice reflection texture to apply to the water's surface.

I have an inverted (flipped upside down) instance of my model rendered for this pass, that is occluded by the ocean layer using ZTest Greater so that only the vertices underneath the ocean show up,

right now i'm testing with a plane, but will replace it with a dynamic mesh. When i view the scene camera it looks fine, but when i view it with the in-game camera any areas covered by the plane are not refreshed and get color smearing as the model animates.

if I turn off the skybox and use a clear color instead it works. What is different about how the skybox renders as opposed to solid color? is there a way to replicate the way the skybox clears?

I've attached the shaders i'm using and some scene screensots below. Thanks for any help, I understand this is a bit of a weird one.

Material applied to the ocean:

Code (csharp):

1.  
2. Shader "Masked/Reflection Pass Ocean" {
3.    
4.     SubShader {
5.         // Render the mask after regular geometry, but before masked geometry and
6.         // transparent things.
7.        
8.         Tags { "Queue" = "Geometry" }
9.        
10.  
11.        
12.         // Turn off lighting, because it's expensive and the thing is supposed to be
13.         // invisible anyway.
14.        
15.         Lighting Off
16.  
17.         // Draw into the depth buffer in the usual way.  This is probably the default,
18.         // but it doesn't hurt to be explicit.
19.  
20.        ZTest LEqual
21.        
22.        ZWrite On
23.        
24.         // Don't draw anything into the RGBA channels. This is an undocumented
25.         // argument to ColorMask which lets us avoid writing to anything except
26.         // the depth buffer.
27.  
28.         ColorMask 0
29.        
30.         // Do nothing specific in the pass:
31.  
32.         Pass {}
33.     }
34. }
35.  

Material applied to the objects in the scene

Code (csharp):

1.  
2. Shader "Masked/Reflection Pass Object " {  
3.  
4.     Properties {
5.         _Color ("Main Color", COLOR) = (1,1,1,1)
6.     }
7.  
8.  
9.     SubShader {
10.         // Render the mask after regular geometry, but before masked geometry and
11.         // transparent things.
12.        
13.         Tags { "Queue" = "Geometry+10" }
14.        
15.  
16.         Pass {
17.             Color [_Color]
18.  
19.            Cull Front            
20.            ZTest Greater
21.                ZWrite Off
22.        
23.         }
24.     }
25. }
26.  

and some screen shots below