Tesselletion "bypassed" by Depth of Field

Hi all, while experimenting with tessellation shaders I noticed that the depth of field was computed before the tessellation pass. At least this is what I deduced from observations, so I might be wrong on the cause.

If you want to try to reproduce the problem

• make a new shader with the Phong Tessellation shader taken from this link: http://docs.unity3d.com/Documentation/Components/SL-SurfaceShaderTessellation.html

• then activate depth of field on your camera. You'll see a result which is different from what you expect.

Now, my rendering path was set to Forward and when I changed it to Deferred Lighting this didn't happen anymore. So I solved it, but I'm a curious one so...

I would like to know:

• Why is the Depth of Field not working well with tessellation in Forward Rendering?

• Why turning the rendering mode to Deferred Lighting solves this?

Thank you very much