- Approach the cache
- Shift+Rightclick the cache as if you were withdrawing seeds from a barrel, for example
- As you are no longer able to shift+rightclick the cache, open the cache
- New items spawn - now you can shift+rightclick the cache again to withdraw all of the items
I think this happens because cache contents get regenerated after it's opened when it's flagged to regenerate.
Is it a possible source of duplication exploits? Maybe... Maybe not? I haven't extensively tested.