(Description on the bug report page)
I tapped lava from a volcano into a holding area in the beginning of my fort and made a channel in the floor above for a magma forge, then covered the channel with a block floor when my floodgate to the lava room didn't close and i was afraid of lava flooding. Later in the fort when i picked up another anvil, i designated the piece of floor to be removed.
When i did so all the items in the adjacent stockpile suddenly vanished, and appeared in the tile right next to the hole. All my dwarves then proceeded to put them back.

I have the save file, i saved right before i deconstructed the floor.
When you load the save, you should see a large stockpile and small rooms with a magma forge and some furnaces, go into the deconstruction menu and remove the single tile of constructed floor adjacent to my only magma forge.
When i exited the game and reloaded the same thing happened to all the items.