Thanks for all the replies!
According to the PNR history, the last change was made at 0653 for a flight at 0725. That change is the noshow process, I assume.
The agent tried to rebook at 0647 (or at least put the remark in my PNR at that time).
To Globaliser and Getafix, that might be the case (I don't have access to neither the fare conditions nor the class of service I flew in), however in this case why would ba.com show that changes are permitted up to departure time in the MMB section?