Smithing Table sometimes flashes red X over output arrow when smithing two stackable items and then picking up the item from the output slot one by one

The bug

When using a Smithing Table with two stackable items and then picking up the resulting item from the output slot one by one, the red X sometimes flashes over the output arrow temporarily before disappearing again. This can be easily reproduced with customized smithing recipes.

How to reproduce

1. Install the data pack below in a world for easier reproduction.

2. Obtain a stack of Iron Ingots and Gold Ingots, and then place down a Smithing Table.

3. Place the stack of Iron Ingots in the first input slot and the stack of Gold Ingots in the last input slot.

4. Pick up the Netherite Ingot from the output slot one by one, and then repeat if necessary.
   → ❌ You will notice that the red X sometimes appears above the arrow before disappearing.