I think once a PO has been approved it is typically locked. You wouldn't want your employee to go back and add stuff to an already approved PO, right? At least that's how it works for us... I have to go into admin mode to make any changes once the PO has been approved.

Yeah I think it does kind of depend, as our's is set up where they can edit POs after they've been approved. I agree though, typically you'd want it so that the PO can't just be edited after approved.