Duplication Glitch that needs to be Fixed ASAP

Duplicating Items 

my friend recently showed me a process of how items can be duplicated in a survival world. The steps were to get a beacon then spam select the item that you want to duplicate in your hotbar slots. The item will be duplicated till it reaches stack of 64. Items like tools and armor pieces can't be duplicated.

 

I am sending a video and a picture. The picture has a red outline of hotbar inventory slots. Please pay close attention to what happens to those items in the video.

 

Thank you