Placing an item into the crafting grid from either the inventory or the crafting table (in creative) and then trying to place the exact same item from the creative Menu into the same slot, where the item from before is already present results in this item getting stuck in place inside the crafting grid. The item can‘t be removed or replaced with another item or be crafted into something else (like Wood planks into sticks). It also stays there even after closing and reopening the Inventory or crafting Table. The only way to get rid of it is by reload the world.