A - The purchase order number used to be 10 digits long. It was extended to 25 digits later. As a matter of fact, if you look at the database schema for the order header, the 25-digit PO number is actually separated into two fields: the PO number (10 digits), and the EDI PO number extended (15 digits). It is these two segments combined together that form the 25-digit PO number as you see in the COP Order Header Screen.
If your invoice form was set up a long time ago, it is possible that your invoice form is still configured to only print the first 10 digits of the PO number.
To resolve this issue, you can edit the invoice form using COP, Util-Setup, Invoice Form Setup, and bringing up your specific invoice form. Go to the purchase order number field -- number 31 on screen 6. If the size is still 10, then enter through this field. The system should automatically switch it to 25. Then save the form and the full 25 characters should print on the next invoice run. See sample screen below.