That's absolute rubbish because I have a PO Box address only on my US account and I make and receive instant payments in the 000's including one earlier today.
AND, I just got a new Paypal Business card and it was mailed to the PO Box no problem. In fact I had asked if they could do me a favour and send it straight here but they said they could only send it to that address!
Sounds like whoever you spoke to doesn't know what they are talking about.