Wow, this thread is exactly what I needed. I booked, yesterday, two business class trips LAX-MAD via BA Avios, paying fees of a whopping $1910.00. I then discovered last night that booking through Iberia is only $554.00 for the exact same configuration (two seats). I tried to transfer my Avios this morning and noted that the 'Combine my Avios' was not appearing. As I was on the phone with BA at the time I discovered this (while cancelling my booking!) I asked the smug representative on the other line and he stated that I needed to have a FLIGHT on Iberia to do it. Good thing I discovered this, as I immediately transferred 1000 Amex MR points to Iberia, and now just have to hope the availability stays intact for the flights we had booked.
$1910 vs $554 - SHAME on BA.