I called in (admittedly contacting the night-crew). The agent contacted the helpdesk, and returns with "Yes, it normally upgrades out of P, unless the flights are very full". The helpdesk were unable to fix it. I pointed out that the site says upgradeable, she said the site follows P, but sometimes P does not get you an immediate upgrade. ?!?!
That's a ridiculous response. If RM didn't want the P seats out there they'd zero the bucket.