NavMesh ignores Static Mesh (builded from BSP)

Hi all! have a problem with generating navmesh. It’s working fine with all standart meshes (default cube, sphere, etc) but not with meshes which was created from BSP brushes. Any solution?

https://forums.unrealengine.com/attachment.php?attachmentid=129536&d=1487193822

4.15 update has fixed this problem.