And rightly so, given your experience. With UA / AC in particular, the two systems do not play well together. On the AC side, there are many long-standing bugs that they don't seem to care to address. The kicker is that when calling UA to inquire about the AC portion of a UA-booked ticket, I'm invariably told to speak with AC, and when calling AC, I'm invariably told to speak with UA. This run-around happens even for issues as simple as seat assignment.

These flights are code-shares in name only, in my experience. And, in my experience, not one of about six such itineraries went entierly without a hitch.

So, I would be quite concerned about booking a ticket when there doesn't seem to be consistency across fare buckets or even offered cabins.