Happens from time to time when the airline tries to force married segment inventory on itineraries. What's interesting about this one is that forcing the separate segments isn't pricing separately (ie both still price YVR-MIA + MIA-YVR) rather than YVR-DFW+DFW-MIA...) but it is changing the available inventory on the flight. The expensive version prices into L on the outbound and K on the return. Forcing the routing in the booking engine drops both into Q.