Ability to edit Date in created & processed PO

User is able to edit Date in created & processed PO.

After reopening PO, Due Date field isn’t empty. PO field is recalculated subject to change PO Date.

To open PO with a changed date, user needs to do the next steps:

1. Create PO, add some Item → Process PO
2. Reopen PO, change PO Date → Save PO
3. Reopen PO and look to the Due Date field