https://github.com/jamespetts/simutrans-extended/blob/b93b03c82c2496c57bf2e5b5f225c9ca2c521e9d/dataobj/settings.cc#L1734
if ((file->get_extended_version() == 14 && file->get_extended_revision()) >= 31 || file->get_extended_version() >= 15)
{
file->rdwr_long(max_speed_drive_by_sight_tram);
max_speed_drive_by_sight_tram = kmh_to_speed(max_speed_drive_by_sight_tram);
}
An error in the if statement suggests that this has not been saved correctly since implementation.
Pull request # 466 contains a fix for this.
Thank you - fix incorporated.