If a stackable item that is equippable has its equipstack set to false, it allows only 1 to be equipped at a time, but when you pick up a stack of an item with these conditions, it will equip the whole stack, rather than equipping 1 and putting the rest in the inventory, or just equipping none of them.
1. Have a stack of an equippable item that you can only equip 1 at a time. 2. Drop the stack 3. Pick up the stack 4. Whole stack is equipped, bypassing the "equipstack = false"