Dupe glitch

After joining my Minecraft world, I dumped all my items into a chest. Immediately after that, I opened my inventory to organize some things, and the game crashed.

When I rejoined, the items I had placed in the chest were still in my inventory. I attempted to put them back into the chest, but the same items were already in the chest as well. I rejoined again, and both sets of items remained the duplicated items were usable and acted as real blocks.