When you click on a recipe or on the crafting book to close the help again you additionally click at your inventory and might pick up or throw items this way.
Reproduction steps for 17w18b+
Use these steps if the crafting help is shown on the left next to your inventory.
- Right click a crafting table
- Put an item in the slot in the middle of the right column of the crafting grid
- Click on left border of the book to close it
→ You picked up the item from the crafting grid
- Open your inventory
- Open the recipe book
- Pick up an item with your cursor
- Click on the book to close it again
→ The item you were holding is dropped on the right side of your inventory