What the bleeping f*?%@ hell is this s?%@t?

Other than that time in Expedia I've never had any other sort of fare conflict on an airline, and I do book tickets on airline sites a few times a year for business.

One time, though, I booked a same day round trip flight Mex City to Guadalajara on Aeromexico. As usual I picked my seats online. The outbound flight was on the usual B-737. The return flight was on an Embraer jet similar to the 737, but with a diferent seat layout. I always pick window seats.

Well, on seeing the plane for the return flight it was another B-737, and my seat was on the aisle rather thant he window. I can live with an aisle seat, but not on a middle seat <shudder>. The question is why the plane wasn't the same the flight schedule and ticket said it was.