Hi all, I've been a long time reader of this forum but this is my first post so I appreciate the courtesy extended to a newbie...

I've done a search on this topic but couldn't find anything that seemed to answer my question, so I appreciate any help y'all can offer.

In anticipation of the traveling for the Christmas holidays I've found a great itinerary from AUS to YWG (that's Winnipeg, Canada) on Yahoo Travel for about $546 flying on NW metal but CO codeshare flight numbers, which is a hundred dollars cheaper than anything comparable I've found so far.

However, when I try to recreate the same itinerary on CO.com I can't pull up the same flights. They exist in the online schedule but the reservation engine refuses to find the appropriate flights. This might be a stupid question, but is there a reason why CO.com won't allow reservations on certain codeshares (it always diverts me to CO metal routings)? I try to book all my CO flights through CO.com for the bonus miles and keep all my intineraries in one place, but looks like CO.com only likes routings that include CO metal.

Here's the itinerary on Yahoo Travel:

DEC 20 - AUS-MSP - CO 5110 (NW Metal)
DEC 20 - MSP-YWG - CO 6622 (NW Metal)
DEC 29 - YWG-MSP - CO 5792 (NW Metal)
DEC 29 - MSP-AUS - CO 5058 (NW Metal)

Any explanation is appreciated... Thanks!