AS (**) 2204PDX 5:00a → SEA 5:57a
F0 D0 P0 I0 U0 A0 Y7 Z7 S7 B7 M7 H7 Q7 L7 V7 K6 G0 T0 R0 X7 N7 W0 E0
AS (**) 2749SEA 9:50a → YEG 12:50p
F7 D7 P4 I1 U1 A1 Y7 Z7 S7 B7 M7 H7 Q7 L4 V0 K0 G0 T0 R0 X7 N6 W0 E0
It's the mixed cabin I think. For a coach fare sold as PDX-YEG, it's probably looking for lowest fare class available all the way across which is L. Mixed cabin can match K and I. If you click one screen further after adding, you'll be able to see the fare codes the website is selecting.