i wonder if it's because that job title has been streamlined, so that all people working in a similar job at the same band are the same?
Personally i can't really see much difference in the 2 job titles, and certainly there is not one that sunds more important than the other, however i appreciate this may not be your concern about it. you are doing the same job, with the same JD and same wages i presume?
Conversely i also work for the NHS but would like to change my job title butthey are curiously resistant,