Description:

When an non-stackable item has its "count" value changed from its NBT, it does not display that in a container, such like a chest, but they are stacked, they just don't show the value, unless you take the item with the cursor, which is a strange and inconsistent behavior, because there's an NBT value that increases the stack count, but when you do it like this, it's just weird, YET it works if you take it out with numbers and then shows a stack number, but not with a cursor, so that's just strange behavior.

However, it does preserve the number when you take it out with numbers on your keyboard, but causes the item to disappear: https://bugs.mojang.com/browse/MC-278488

Re-production steps:

1. Give yourself a Netherite Sword
2. Place down a Chest
3. Put the Netherite Sword anywhere in the chest.
4. Stand on top of the chest
5. Run: /data modify block ~ ~ ~ Items[0].count set value 5
6. Take the Netherite Sword out by clicking on it with the mouse once which makes the item follow your cursor to move it to a different slot.
7. Observe how it says "5" on the Item, but how it didn't have a number before at all

You can additionally test it with the Test Game that I attached.

Bug Repro NBT Count Chest.zip

Expected Result:

I expected that the Swords would show a 5 next to it.

Actual Result:

The sword only showed a 5 once I took it.

nbt_count_bug.mp4