I suppose you're quite right... now that I think about it, I've never had a straighforward experience booking on IB, regardless of mechanism. Last time I wanted to make a revenue booking in Business, and Iberia's web site and phone reservations both seemed to imply the flights were sold out. Of course third party booking agents, travel agents and AA.com were all able to quote fares and even seemed to confirm seats available.

Eventually, I made one booking with AA (had to twist their arm to do it) and another through a travel agent (who happily did so in exchange for a service fee). All the while, IB treated the flights as sold out... and wouldn't sell me a ticket directly.

I was naive to think that it would be low-hanging fruit for IAG to make the left hand's airline start using the same reservation system as the right hand's airline...