Problem with texture coordinates

Sometimes, when i select a face from a brush for tile texturing i have the problem of his coordinates get crazy. The tiling up to thousands and finally just see one color instead the texture. I dont know why. Only in specific brushes, i think could be because they are not planar but even i try to fix the faces moving points not working as i wish. Could you give a help with this issue?
Thanks a lot.
Sorry for my english

Ivan