This sounds like the issue that was fixed in SVN 9274 where the Wanted promotion was making criminals attackable. Presumably when you moved the Horse in, the Thief was not yet Wanted, but by the time you moved the Buffalo in, it was.
Fixed King Richard's Crusade! I made all three of the changes I mentioned in my previous post, and successfully got a Crusader to spawn 16 turns after I made the changes. Interestingly enough, the Crusader did not get all of the XP that it would have if it were a conventionally trained unit, but that's presumably a problem somewhere in the addProductionExperience function and not really important. It was created with all the correct promotions for the city, but only around 110XP, whereas new-build Melee units in the city start with well over 200XP. My current game looks to be on track to obsolete the Crusade wonder before the timing for the next one hits even if I delay Liberalism as long as I can, but it appears to be working at least. From a balance perspective, I think the game speed scaling on the spawn rate could use a look in light of the changes to game speeds, but that's a very minor issue really. As it currently stands I believe that on all game speeds except Normal it'll wind up being one Crusader every 16 turns. Not sure what the intended rate is supposed to be, and Crusaders are quite powerful, so it may be fine just the way it is. The line I commented out may be meant as a further random limit on the spawn rate of Crusaders, but I don't really see a need for it.