Your assumption may be correct, but in my experience the coding of QF codeshare flights deep in the BA IT system is flakey at best (based on my experience as QF with a BA code). That I expect it will post incorrectly, but will be quickly fixed once you put in a manual claim.

(This BAC is so unbelievably complex that they have struggled to code anything beyond prime flights. Just think about it for a moment...).