A consumable item with the same ID as another can convert the second's damage value into it's own

If the player has two consumable items with the same ID in their hotbar (e.g., a golden and enchanted golden apple), the first can convert the second's damage value into it's own if the selected slot is changed to the second while eating the first. So, if the player was eating an enchanted golden apple, tapping the slot containing the golden apple will change that golden apple into an enchanted golden apple.
Stacks are unaffected by and have no effect on the issue.

Tested in both Creative mode (potions) and Survival (fish, cooked fish, potions and golden apples.