Large Terrain scene subtractive brush issues

Hello, I am glad I found some one to talk to. I have a big Terrain scene and I am trying to use the Subtractive brush on a portion of that terrain and it shows up as an invisible red outline but it does not cut out of the terrain. I have noticed this issue on other boxes when I have a lot of things in my scene.

Just a side note, I am making a game at the moment that is very large. What an amazing engine:) I am excited for 4.1:)

Subtraction brushes only work on other brushes. Think of the Terrain as static mesh you can edit in the editor. Also large brushes do cause some issues. I know they are working on it.