So the thing is just to be aware of this functionality. The easiest way to check your work is to see what location is listed in your new item--if it's your location, you're fine, but if it's a different school, you'll want to either A) change the location (you'll also have to click the "Circulated By" box and change that location); or B) click the Clear Fields button in the lower right, which will wipe out all the information and give you a clean slate. Here's an example of a copied item:
Of course, if you are adding multiple copies of a title, this makes it a lot easier - just select the item you want to copy, scan your barcode, and click "Save and Add Another." Makes it much faster!