Have you ever printed a PO and noticed that the Second Description line and Vendor# data for the last line item is duplicated at the bottom of the printed PO and in the database??
 
We have, and it took me looking over the shoulder of the Purchasing Agent to figure out how she was doing it.
 
When you are finished entering a PO, press enter one extra time to move off the REF field and into the Item Number field.  Save the PO with the SAVE button, and then view the PO.  You will find that the Second Descritption line and Vendor# information shows up two times. (Maybe the MFG# also, but we do not have that many items with that field filled in).
 
Pressing ENTER that one extra time caused the blank item line to be saved along with the Second Line desctiption and Vendor# from the previous line item.  The variables that hold these values appear to only be updated after the Item Number is entered.  If no Item Number is entered, then they still contain the previous values.  
 
Only one person around here was generating PO's with these extra lines because they routinely pressed enter one too many times before saving the PO.