If I scan an item, and the look-up takes a while to complete, I move on to entering the next item while the previous one is still being looked up. If I'm in the middle of, say, typing in a book's name or ISBN because it has no barcode, and the earlier item finishes being looked up, I am whisked away from entering data and made to look at the earlier item's info. This is bad. Please fix it.
Worse, any data already entered is gone when I go back to the newer item. This is very bad. Please, please fix it.