Bug allowing duplication/multiplication of stackable items.

As the title says, this bug allows duplication (in fact, multiplication) of stackable items. For example if you have one diamond, it can become many diamonds. This could easily break a survival world. But you have to have a beacon to be able to do it.

1. First you have to go to Settings > Video and change the UI profile to Pocket (not classic).
2. Then find your stackable item (for example: a diamond) and put it in any hotbar slot (one of the first 9 inventory slots).
3. Then open the beacon interface and quickly double tap the item. It will become two. Then if you do it again it becomes four. And so on...