I notice that after playing Creative Mode for a while, something odd happens. And this isn't reset by closing the program, and starting it again. It is only remedied by generating an entirely new map. After a time, I can't change my 9-item inventory bar. After pressing E to bring up my inventory screen, if I click on anything in the 9-item inventory bar it instantly disappears, rather than being picked up and able to move to a different slot. If I click on an item from the grid of items I can add to the inventory slot, it picks it up, but it says 64 beside it, NO MATTER WHAT ITEM IT IS! Even worse, I can NOT PLACE IT INTO MY 9-ITEM INVENTORY BAR! What I already have in the bar CAN BE USED, but nothing can be added to it, only removed. And the only way to fix this is to go to the world creator in Minecraft and have it generate a completely new Creative Mode world, and then play that world. Since the bug seems to be stored in the world, the old world then is completely useless and so should be deleted. But eventually the new world will bug out too. It's only a matter of time.
Why isn't this fixed? I have the latest minecraft.jar. And why called the "shift" bug?
Ask Mojang.
It is called the Shift click bug because basically it happens when Minecraft thinks you are holding down the shift key when you really aren't. It's not entirely the fault of minecraft, it is also communication with your computer to minecraft. There really isn't a way to fix it permanently (at least as far as I know). It has been around since the beginning stages of minecraft, because I always remember placing stuff in chests with a shift-click bug issue.
basically what deadly said, and about 'fixing' the problem, just press the right-shift key + right ctrl, usally allways fixed when you do that.
WoM Coins: 1275
This is called the shift bug. All you need to do is hit f11 to go into full screen, then hit it again to get back out of it. Problem solved, no need for a new map...