Landscapes Do Not Recognize Material Layers if Blend Assets Are Added in Material Instance

*Developer's Note*  - Material layers are not landscape layers and are not expected to interact.

Not sure if this is a bug, but depending on how a layered material is created, its layers may not be recognized by landscapes.

If you create a layered Material and assign Blend Assets to the Layer Stack, and then create a Material Instance from it and assign the MI to a landscape, the landscape will recognize the material layers.

However, if you create a layered material without assigning any Blend assets in the layer stack, then create a material instance from it and assign blend assets in the Material Instance, a landscape will not recognize the material layers.

1. Open attached Project
2. Select Landscape, go to Landscape editing mode, Paint tool
3. Observe that Target Layers shows material layers from MI_Layers
4. Now assign MI_None to landscape

Result: Landscape painting tool's Target Layers no longer show material layers from MI_None

Expected: Both Material Instances will have layers since they have the same setup