Ingredients in custom recipes do not remain on the crafting grid even if specified to do so

Making a custom recipe that returns more than one result, all but the first of which match some of the recipe's ingredients, doesn't actually keep the ingredients in the crafting grid.

How to reproduce:

The attached behavior pack contains a recipe that turns a stick and a piece of string into a stone block and a piece of string.

1. Open the attached file to add the behavior pack to the game.
2. In the world creation screen, go to Behavior Packs and add the imported pack.
3. Create the world.
4. In your inventory, put a stick and a piece of string in the 2x2 crafting grid.
5. Take the stone block out of the result slot.
   → The string is consumed.

Expected result:

The ingredients that were specified as both ingredients and results would remain in the crafting grid.

Observed result:

All ingredients were consumed.