Adding a 3rd Grass brush ruins EVERYTHING D:

I'm designing a world for a uni project, and I'm experiencing severe issues with the grass brushes. While 2 brushes work excellent, adding a 3rd brush fraks up all implemented grass.

Doesn't matter if it's a detail mesh or grass texture, doesn't matter if i used it or not. The mere presence of a 3rd brush and the following error appear:

All brushes are set to CLAMP

Any help would be highly appreciated,

Cheers,

vedsten