There are two ways to create a new line item on a PO. The first is from the item layout, using the button in the lower, right corner: Create Order. This will add a PO line to an existing PO if that status is "New." Otherwise, it will create a new PO.

Creating a PO line from the Item

The second is to use the Add button on the PO layout.

Creating a PO line from the PO

Although the results of the process should have been the same, regardless of where the PO line originated, there were slight differences. These have been fixed so the process now produces the same result.