Bundles can end up being stacked, causing item duplication

You can duplicate any items using bundles. All you have to do is store x (up to 16) empty bundles in a bundle A (see attached picture 1). Then fill your inventory so there is no more slots available to pick up items (see attached picture 2). Then you unload your bundle A by right-clicking on it. Since you have no more slots available in your inventory, the 16 bundles previously stored in A will drop.

Now, free one inventory slot. You are now able to pickup the bundles previously stored in A. But you will have a stack of x empty bundles (even if bundles are not supposed to be stacked) (see attached picture 3). Then pick the items you want to duplicate (for example 64 diamond bloks) and store them in the stack of bundles by hovering it with the items and right clicking. You can now pick the stack of x bundles containing 64 diamond blocks and by right clicking around in your inventory, you will separate them (see attached picture 4). You will then have 16 bundles of 64 diamonds blocs. You multiplied you diamonds by x (see attached picture 5).