I don’t know if this is a bug or an oversight, but I was messing around with a custom enchantment that could go on saddles and harnesses to increase the speed of the mob being ridden. It increases the movement_speed and flying_speed attribute of the mob with the item. The enchantment shows the proper tooltips saying it increases both those attributes when saddled, but only mobs that actually wear saddles seem to have their movement speed increased. Applying the enchantment to a harness and putting it on a happy ghast seems to do nothing to increase their flying speed. Seems like whatever checks the “saddled” condition isn’t accounting for it being a harness or something like that.
Ok, so upon more investigation, it’s in the “body” slot, not “saddle”. So, not sure if that’s where it’s supposed to be or not. It doesn’t feel wrong per se but doesn’t feel consistent with how every other rideable mob uses the saddle slot