So, imagine you have sandstone in hotbar slot 1, and an iron block in hotbar slot 2. If you open your inventory and hover over the iron block then push the '1' button (if you switch them around manually it works as normal - you need to use the shortcut keys for the glitch to happen), the two switch around, as intended. But then, when you place the iron block it appears momentarily before turning into a sandstone block. This even remains when you break the blocks - it is still a sandstone block when it drops. (I had to discover this the hard way - a diamond block in my house turned into dirt) Note that if you do exactly the same thing, and place the sandstone, it does NOT turn into iron. NOTE THIS ONLY HAPPENS IN CREATIVE MODE (If you switch the blocks in creative, and go into survival, and place it, it still works as normal)