1. Run a game in Creative Mode.

2. Grab a bunch of items(anything stacks in 64).

     e.g : 18 stacks ironblock

3. Drop  them with ctrl + q or q.

4. Expect to see all items, but it would always disapper some of the stacks.

    e.g 18->13 losing 5 stacks.

This bug can also be reproduced on 1.16.5+.

Version below 1.16.5 haven't been tested.