Made me find another bug on BA.com. I can't book AMS-KEF....
We are unable to find seats for your journey. The most common reasons for this are:
You may have requested a route that we do not operate at that time of year.
We may not fly to the destination you have chosen.
Your journey may require more than six flights; you can only book up to six flights on ba.com.
I can book them fine separately though...