HBG do not reproduce GSF. HBG reproduce a mixed genetic spectrum somewhere between a BG and a GSF. Some of their offspring may look more like BG, certainly some of their offspring will certainly look more like GSF...

Mixing pure BG with HBG may result in mistaken ID between them and a resultant cross between them. This is particularly true if you have crowded spawning conditions and murky water. If you have fairly clear water and spawning areas that aren't crowded, the crossing will be reduced but will still occur.