The bug
If your mouse is moving an enchanted item, the debug pie will have a weird purple box around it. It goes away if you have a potion effect, however.
Steps to reproduce
Open debug pie (Shift+F3)
Open your creative inventory.
Click on an enchanted book to move it around. (Don't click it into another inventory slot, though.) --> ❌ Notice the purple box around the debug pie.
Discovered while testing and related to MC-218596.
@markderickson, I noticed you changed the summary, and I was unable to with an item that was not a book. Were you able to reproduce it with an enchanted item that was not an enchanted book?Edit: Never mind, I tested it again and was able to reproduce it with a non-book enchanted item.