Material param reset bug on landscape

From licensee:
When a material instance is applied to a landscape in a scene and the user resets param in that material instance, that edit is not applied to rendered landscape (while it is if the material instance is applied to a static mesh).

I attached athe project and a screenshot of the problem. If you load the project's Untitled map, you see a white box and a white landscape.

Set Param in NewMaterial_Inst to 0, manually. Box and Landscape are now black.

Reset Param to its default , by presseing on the reset arrow next the the value of Param.

Cube is now white again, while landscape is still black.