Ghulam Cavalry: "{SPEARMAKER3, HORSE_BREEDER3}"
Mounted Sergeants: "{SPEARMAKER2, HORSE_BREEDER2}"

Yet they gets their bonuses from the Horse Breeder line. I am wondering if the Horse breeder is the exception to this rule? I remember testing this quite a while back rearranging the order of building types and made some interesting discoveries, I can't remember it now though or where the thread/post was.

There are very few units that actually make use of a pair of either a swordsmith, bowyer or spearmaker anyway. At the moment only the Futuwwa, "{BOWYER3, SWORDSMITH}", spring to mind.

Also if units actually require a master level building to build, e.g, {SPEARMAKER4}, they seem to lose the valour bonus from it.