The bug
When switching to another stack of the same item while consuming (eating / drinking) a consumable item, the eating animation continues, but no item is consumed, no hunger is restored and no effect is applied.
To reproduce
Get two stacks of the same food in your inventory
Select the first one
Start eating from it
Switch to the second one while eating
→ ❌ The animation continues, but the food is not consumed
Video
[media]Related issues
discovered while testing
Attachments
Comments

Also affects potions / water bottles / honey bottles.
Also affects milk buckets.
Confirmed for 19w44a.
Confirmed for 1.15-pre1.
Confirmed for 1.15-pre2.

In 1.16-pre2, animation is restarted when switching to another stack of food.
Cannot reproduce in 20w49a.
Cannot reproduce in 20w51a either.