I suspect that this is just a website bug, but I must admit to being a bit nervous to booking anything right now, w/o knowing what's happening!

When booking a TPAC itin that includes a North America segment codeshare on AC, UA.com seems to be advertising/selling non-existent fare classes. For instance, a search from YYZ->BKK on 6/24 yields several codeshare segments, including UA8293 YYZ-SFO.

UA offers First (F) as an option for that segment. However, AC doesn't have a F class bucket! They sell their own flight as a C or D fare, depending on which Executive flex option you select. Likewise, on the MileagePlus site, the partner earning tables for AC don't have F even listed as an option.

Perhaps more worryingly, the site will also try to sell you a First (F) fare on AC express flights that don't seem to have an F cabin. So I suspect that actually booking this would be a recipe for chaos upon check-in...

Anybody seen this before, or had experience in what happens if you book?