This happened in Singleplayer survival.
Nothing was supposed to happen.
I had a full inventory and I tried shift clicking items out of my hotbar into my inventory slots not realizing that it was completely full. It shouldn't have done anything but the items just disappeared. I tried it over and over again and it kept trashing my items.
Steps to Reproduce:
1. Fill up your inventory completely.
2. Shift click an item in your hotbar that doesn't match any of the items in the rest of the inventory.
Dupe of MC-88929