As well all know, sometimes Minecraft fails to update when a block is broken, and an invisible block is formed, where the user will get pushed back.

In earlier versions of Minecraft, the user could place a block where the invisible block was, and the block would turn into the block the invisible block was supposed to be.
Eg. if you were mining nether rack fast, and it glitches, you could place a nether brick there, and the invisible nether rack would reappear.

Upon mining the invisible (now visible) block, the player would receive both the glitches block and the block placed.

In the snapshot versions, the block would turn normal again as previously, but also eat up the block the user placed to restore the block.