Saddles equipped on horses cannot be replaced without removing them first

The bug

A saddle in a horse's saddle slot cannot be replaced by a different saddle held by the player's mouse cursor. Horses, donkeys, mules, zombie horses and skeleton horses are all affected by this issue. Horse armour is not affected.

How to reproduce

1. Summon a tamed horse equipped with an enchanted saddle:

   /summon horse ~ ~ ~ {Tame:1,SaddleItem:{id:saddle,components:{enchantment_glint_override:1}}}

2. Attempt to replace the horse's enchanted saddle with an ordinary saddle
   → ❌ The enchanted saddle cannot be replaced without removing it first