Using /give to make a bundle that contains more items than naturally possible allows items to be duplicated by trying to put another item in the bundle. The item that you try to add to the bundle then turns into 64 or sometimes more of itself. It also means that items like tools and ender pearls can be stacked to 64.
To reproduce
Run
/give @p bundle{Items:[{id:"minecraft:dirt",Count:64b},{id:"minecraft:dirt",Count:64b}]}
Give yourself a diamond (or other item)
Right-click onto the bundle with the diamond
→ ❌ The diamond's item count increases
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We're tracking this issue as MC-225381, so this ticket is being resolved and linked as a duplicate.
That ticket has already been resolved as Won't Fix, which means this is considered a bug but won't be fixed. The description of that ticket or the comments might explain the rationale. Please do not leave a comment on the linked ticket.
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