ive encountered a duplication system.
For example: When jelly berry is in the action bar and there are empty action bar you can duplicate the jelly berry.
How it works for me is that when you eat the berry and you use the scroll button to go to another empty action bar there are times that the berry is duplicated. It's very hard to time but it can be done.
It can work on any item but the other items are hard to duplicate. This can be an abusive system as you don't need to gather resources.
So hope this can help the devs.