Im guessin because people on the forums complained about not having 1.8, and that we are meant to bug test. Until Notch gave up and released it how it was. Now we have you and the vast majority of the forums complaining about bugs. Maybe thats why.
In creative mode for servers I got almost the same bug.
When I trying to select a block/item in the list and try to place it in my action bar, it wont be placed.
But If I drop the item out, and then pick it up, I got it. If I try to drop it from inventory, it dosn't work. So I have to use drop shortcut.