I noticed a strange bug when using the Landscape grass function in the a landscape material in combination with the Landscape LODBias.
It seems to work fine when I change the LODDistance Factor in the Landscape actor but completely breaks if you select a single component with the component select tool, go to the details tab and change the LODBias of that component to something like 5.
It looks like it still works but as soon as you touch landscape and start painting or sculpting over that affected component the landscape grass disappears and is spawned way above the landscape actor in the sky.
I tested that in the latest Unreal build 4.15.1.
Regular foliage is not affected by this btw. only Landscape grass type.