Duplication glitch

When I started my survival world,I found sugarcanes. So I harvested it,and got 9 sugarcane.
Then a little while later,I exited my new survival world to have a break. When I came back to the world, I noticed that the sugarcane was still planted there right beside the water. And in my inventory was the 9 sugarcane that I just harvested earlier, before I left the game.
What I expected to happen, was that I could harvest the sugarcane,and make a sugarcane farm later in my world.