You type or paste the Title and hit enter or tab to go to the Author field; you type the first letters of the surname, select the right author from the shortlist, and there is no time to hit enter or tab because suddenly the focus is lost and you're not editing any fields anymore.

This makes it annoying to add new items by hand. The behaviour is also not in line with what other input fields do: the book title field for example does allow me to select the relevant book and then keeps editing focus, so I can easily tab to the next field.