When a new Tag is added to handle data of an item on Vanilla, if Spigot already handles a tag of the same name in a tag already implemented, that item will lose that data on interaction until specific ItemMeta is added for that item.

This means that whenever an existing Tag is added to an item, Spigot servers will suffer of data loss issues instead of just needing a 'New Feature' to make it accesible with the API.

Being something that will cause issues everytime that happens, this should be fixed to prevent that from happening on future versions.

The issue is caused by the ItemMeta class only handling the Tags specified for that Meta but also not as an unhandledTag as is technically a handled tag therefore making that data dissapear.

https://hub.spigotmc.org/stash/projects/SPIGOT/repos/craftbukkit/browse/src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaItem.java#392

This issue caused this already fixed bug, and if not fixed, will cause similar ones on the future.

https://hub.spigotmc.org/jira/browse/SPIGOT-5907