Originally Posted by
bhbloke
In an ideal world BA have realised that to get more business travellers in CE they need to offer this option to keep up with Easyjet.
In the real world I'd wager that Ldnn1 is right
A bit of further research turned this up:
https://www.flyertalk.com/forum/28306840-post13.html
Which suggests the same day change was extended to domestic and LGW CE bookings, but not LCY or LHR. Mine was certainly LHR so it appears to be a new thing (since May) or a glitch.