When I A On Survival I Was Goin' To Build A House With Cobble, What I Didn't Know That It Was Already On My Hotbar, Then I Did Put My Stack Of Cobble On My Hotbar, Then I Realized That Why I Have 2 Stacks Of Cobble I Only Have 1 Stack, So It Was Duplicated or Something. (In Fact It Was Glitched)

Steps To Reproduce Bug:
1.) Put (an) item/items on your Hotbar
2.) Then Try To Switch Places In Your Hotbar
3.) Sometimes You Will Have It 2 to 4 duplicates. (the item / items you've switch places was duplicated)