when i do a simple patch mesh on my ground brush to create hills and stuff it all works fine until i press v, then it makes the brush all flat and it goes into a wall and you cant stretch it out or anything, so basically you cant even see it and it gets rid of my ground brush

The same problem was happening to me. The only way that I could figure out how to fix it was to simply try and make another one. I'm not sure what the cause of the problem is but if you try and make the brush larger before turning it into a patch, it might work.

uhhhh anyone?