Items can vanish when using bundles with max_stack_size above 1

Steps to reproduce:

1. run the command /give @s minecraft:bundle[minecraft:max_stack_size=2] 2
2. spread out the two bundles
3. put one of the same item in each bundle
4. stack the bundles together again
5. take out the items

Observed result:
Only one item comes out, the other is lost

Expected result:
The other item does not get lost