Landscape 'crack free displacement' option causes landscape layer coords and UVs to be wrong

If you check the 'crack free displacement' option in a landscape material,
it seems to break the results of both the landscape layer coords and
regular UV input node. Worldposition is not affected.

Strangely, the difference only shows up in the vertex shader itself (so the
displacement shows it).

Here is a material with crack free OFF:
[image: Inline image 3]
note that displacement matches the basecolor (which is the heightmap
texture). This image is correct.

and with it ON:
[image: Inline image 4]

The displacement appears to go away, but if you zoom out you can see it is
actually just sampled at the wrong scale indicating the UVs (or in this
case landscape layer coords) got messed up:

[image: Inline image 5]

I did drastically increase the displacement intensity in this last image to
make it obvious what is happening.

Tested in binary 4.8.3 and 4.9.2 and the issue occurs in both builds.

1. Open the attached project.
2. Select the Landscape and open the material.
3. Within the Tessellation section, enable and disable 'Crack Free Displacement'

Outcome: Landscape displacement is wrong.
Expected: Displacement remains, and cracks from displacment are better hidden.