I believe that this gem first came from HIDDY.

I have just bought a return LHR - MAD - VGO.

All on BA tickets, LHR - MAD is BA metal the rest are IB. I was able to reserve a seat (exit row) on the BA flight but the IB flights would not show seat selection on BA.COM. I went to the IB sight, no seat selection available. I called the Silver line and they could not select seats on the IB sectors. I went to Finnair and was able to select seats (exit rows excluded) on all the IB sectors. I returned to the IB site and saw that they were showing the seats I had selected via Finnair on my reservation.

Lets see what happens.... more next week!