Landscape Hole material + Grass Tool

Hi! I am using grass tool to spawn foliage on a world composited map, and using it on a landscape with grass node in it will make grass disappear around the hole in a zone of about 30-40 meters.
Is it a bug or something similar?

Thanks.

It could be your brush falloff. Change the falloff to 0, paint and check the results.

Why should it be the fallof? However I tried again and it worked. Maybe I was making something wrong.