Inventory Items Glitch

When I open a world, it loads ok, but when I try to get something from the creative menu the item doesn't move. (If I'm on a tab, "Building"/"Miscellaneous", etc, and I want to move an item to the tab, deleting it, it won't work). Watch the video I linked. If there's an empty space on the menu, the item goes there, but if there isn't, the item goes back to my inventory (which is VERY annoying). Also, when I press shift (to get a stack of items) it doesn't do anything....