Put a bundle in a decorate pot in the creative mode and break the pot to take it out, so you'll have 2 bundles.
And when I put an item into the original bundle, the item will also in the duplicated one.

Steps to reproduce:

1. Put a decorated pot on the ground.
2. Put the bundle with things into the pot.
3. Break the pot and pick up the duplicate.
4. Put an item into the original bundle.
5. You will see the same newly placed item in the duplicated one.