cut away shader problem - forward facing pixels are not rendering properly -

The problem is shown below, the cut section is displaying fine but when the model is orbited around its swapping between which faces are getting rendered when they actually all should be.

View attachment 112554

Shader "Custom/CutAway"
{
Properties
{
_MainTex ("Texture", 2D) = "white" {}
_section ("Section plane (x angle, y angle, z angle, w displacement)", vector) = (0,0,0,0.15)
_Color ("Section Color", Color) = (1,1,1,0)
}

SubShader
{...

cut away shader problem - forward facing pixels are not rendering properly -