Yesterday I encountered another of that pricing mysteries:

WestJet informed me that DELTA, their partner on Boston-Toronto direct route, just canceled the DL4174 (which I booked in January) under shared code (WJ6307), by the last day of August. So I needed to find another way to get to Toronto on Friday 11th of October. I found an X booking class via DTW -or- JFK for the same price of $137. It gave me only 35 minutes in DTW to make the transfer and the recent flights were coming and going to/from different terminals, so I elected to go via JFK which gave me 1 hour and 13 minutes and do not currently involve a change of the terminal.

Once I hit the button with my credit card filled in, the system told me: "Sorry the price just went up to $222". So I went back and wanted to book via DTW, but the same thing happened. Frustrated, but in need of the ticket, I did book the JFK route for $222 in T class. When I checked this morning, I did not find the same routing any more (DL 879 to JFK and DL 4157 to YYZ)!! But when entered manually with Advanced Search, it did find the same routing for some $270 in a higher class.

At this moment, I am looking back and the T class is back for $222, and it does pop in the first search (by price).

I feel like playing slot machines.