Replacing an allay's main hand item with another item of the same ID does not update the displayed item

Summon an allay.

/summon allay ~ ~ ~ {NoAI:1b}

An allay is summoned.

Give it an item

/item replace entity @n[type=allay] weapon.mainhand with stone

The allay is holding a regular stone block.

Replace it with another item of the same ID

/item replace entity @n[type=allay] weapon.mainhand with stone[item_model="dirt"]

The allay is still holding a regular stone block, but it should be holding a dirt-model stone block.

Rejoin the world
The allay is now holding the dirt-model stone block.