A similar thing happened to me in January, when I booked a ticket from ORD to SIN (for travel in March) on UA/SQ. On Saturday evening, the price was $1600 but I didn't buy it since I wasn't sure of the dates. By the time I decided to buy it on Sunday morning, the price for the same itinerary jumped up to $4000. Luckily I decided to wait and the price came back down to $1600 on Sunday night when I bought it.