In 1.20-pre2, MC-124327 was fixed. This means that when renaming an item in an anvil into an empty string resets the custom name.

However, items whose custom name has been removed in this way do not stack with items that have never been renamed.

To reproduce

1. Get a stack of items
2. Rename half of it in an anvil (to any name)
3. Rename that half again, by making the name field in the anvil UI blank
4. Try to combine the two halves of the stack again

Expected behaviour

An item whose custom name has been removed by renaming it to an empty string would stack with other unnamed items of the same type.

Observed behaviour

Even though the custom name has been removed, the item retains an additional NBT tag, which makes it unstackable with items that have never been renamed.

Video

Minecraft 1.20 Pre-release 2 - Multiplayer (LAN) 2023-05-17 23-45-22.mp4