When crafting firework rocketss and firework stars, if you have different sized stacks in the crafting window, shift+clicking to craft all of the item will craft multiple types of firework rockets or firework stars.
Examples:
Rockets:
2 gunpowder + 1 gunpowder + 2 paper
Mousing over the result says "Flight Duration: 2". Shift+click will craft 3 of those and also 3 with "Flight Duration: 1".Stars:
2 gunpowder + 2 cyan dye + 1 wither skeleton skull
Mousing over the result says "Creeper-shaped". Shift+click will craft 1 of those and also 1 with "Small Ball".
I noticed this result first in a multiplayer survival world at a crafting table. I then went into a creative single-player world and tested at a crafting table, changed to survival, and tested in the inventory. This happened each time I tested.
First, I disagree with this being marked as a duplicate of MC-17431. Even if the underlying cause is the same, neither MC-17431 nor any of other issues marked as duplicates of it mention a bug during crafting; all of those issues talk about what happens when you move items into the Enchanting Table GUI.
Second, I've now tested this in the latest snapshot (20w21a), and the bug persists, so it wasn't fixed by whatever fixed MC-17431. @Galaxy_2Alex , because this persists, can you please either reopen this issue or reopen MC-17431 and add this information?