Transparent object VS itself

Shader issue, here. I tried to modify unity’s toon shader a little bit to make transparent/translucent objects. The modification is just changing the render queue and type to ‘Transparent’ and add ‘ZWrite On’ and ‘Blend SrcAlpha OneMinusSrcAlpha’. But from YOURFILELINK.COM and YOURFILELINK.COM you can see that it works well for objects on different meshes, but not the same mesh. I wonder why. Thanks. (The model is two semi-planes, each has a red triangle and the rest part is transparent).

I posted a similar question but didn’t upload any image there.

Now I used a method of AlphaTest to walk around. Please refer to for details.