PE upgrade price question

Sorry for the vague title but wonder someone could give me an explanation.
Off to Las Vegas in February 2010 and had originally booked PE outbound (6th Feb) and Y inbound (13th Feb). Since the booking and with the current sale I wanted to upgrade to PE on the inbound sector.
I clicked on the upgrade button on my booking screen (for 190) and I get the following message;
'The upgrade you selected is no longer available.'
I ring reservations and an Indian chappie tells me that I can upgrade for 530!!!! So I declined the offer.[:0]
However if I do a dummy booking I can get a return for 813 which is is what I would be paying in total if I upgraded the inbound sector for 190.
So can anyone explain the discrepancy?[?]
ADDITIONAL: I also checked Expertflyer and it appeared the flight is wide open.
Off to Las Vegas in February 2010 and had originally booked PE outbound (6th Feb) and Y inbound (13th Feb). Since the booking and with the current sale I wanted to upgrade to PE on the inbound sector.
I clicked on the upgrade button on my booking screen (for 190) and I get the following message;
'The upgrade you selected is no longer available.'
I ring reservations and an Indian chappie tells me that I can upgrade for 530!!!! So I declined the offer.[:0]
However if I do a dummy booking I can get a return for 813 which is is what I would be paying in total if I upgraded the inbound sector for 190.
So can anyone explain the discrepancy?[?]
ADDITIONAL: I also checked Expertflyer and it appeared the flight is wide open.