As QE2 was steaming towards the Falklands she was an RMS.... either that or the shipboard printers got it all wrong...
Just as a matter of interest - wouldn't QE2 have had RMS painted on her bow, on her stern, on the wind scoop, and even more importantly engraved on her builders plate, had Cunard wanted her to be referred to as a Royal Mail ship?!
Holy Nougat confirms above that the prefix RMS wasn't used on her logs and other legal documentation.
Flagship confirms above that Cunard didn't wish her to be classed as an RMS.
Perhaps it wasn't corrected formally, because for some people (possibly the printers et al) the prefix might have been a convenient way of maintaining a particular sort of status?