Ah, could this be a trip which started on AA or another airline? Or indeed the document check if going to the USA. In which case this is quite normal and to do with different booking systems being out of sync with each other. It helps actually, since if he is checked in it speeds up the boarding pass delivery. It is also possible that if left a few hours BA.com or the App may do the necessary but it's no big deal, you can't get to Flight Connection security in T5 (anywhere) without a BA staff member checking your boarding pass, they can print or reprint boarding passes in all but the most problematic of cases. At T5B and T5C if they have such a case they ring up someone to clear any blockage, at T5A there are customer service desks along the wall in Flight Connections.