Foliage disappears when building floor on it

After making foliage with any static mesh, in game if I build a floor on the ground which has foliage on it, the foliage disappears. I can build any other piece on the ground, foliage does not disappear. I tried to record it, hope it shows my issue. Is there any setting to the static mesh or the foliage which I need to do or is this a bug?

Video of my issue