Preferred Seating not chargeable on A380 SIN-HKG?

[Saracen]

I checked in online for my SIN-HKG flight on the A380 earlier today and selected 71A (I think). I got a dialog saying it was Preferred Seating and would cost, but then in the same dialog, under cost, it indicated $0. In the T&Cs it mentioned $50. I clicked through and completed checkin and was never asked to pay. What gives? Is this a website bug? Will I be charged at the airport? If so I'd rather take a normal seat, but it's too late now!

[SINFJ]

Preferred seats is open for booking up to D-48 when OLCI opens. If they open it as available at OLCI then it is not chargeable.

[Saracen]

Thanks, I wasn't aware of that, as I thought they sold it at the airport too.

Thanks for clarifying.

[EWR]

Thanks, I wasn't aware of that, as I thought they sold it at the airport too.

Thanks for clarifying.

Is 48D on the new version of the A380 a preferred seat? It seems not to be a chargeable seat as I can click through during booking (>48 hrs before dept). The actual seatmap for selection is different from the generic seatmap you find on the Fleet webpage.