Moving blocks in creative inventory with number keys

A bug discovered by this guy: http://www.planetminecraft.com/blog/new-glitch-with-video/. Basically, when moving blocks in any part of the creative inventory, except the Survival inventory, with the number keys, when you place the recently-moved block, it places the correct block, then a split second later, whatever was originally in that spot in your inventory that you moved the block to gets placed, including air.