I observed that chest items with custom data (e.g. a custom name) occassionally have an unexpected "minecraft:container": [] component added to them. I consider this component unexpected, since when trying to manually add such an empty container component to an item via the Minecraft /data command, the component is omitted (probably because it equals its default value).

My current guess is that the component is added somewhere during the Bukkit<->MC ItemStack conversion. Reproduction example

• Rename a chest item in the anvil.
• Check the nbt data via Minecraft's /data command:The item has a custom_name but no empty "container" component.
• Drag the item inside the player inventory. This isn one way to trigger the MC<->Bukkit ItemStack conversion (due to the inventory event).
• Check the NBT data again: It now has the empty container component.

Items with and without this empty container component are considered different items by Minecraft: They don't stack inside the inventory.