Natural Sort Order not working for Roman Numerals

[topbanana]

I have a few movies where each part is named/numbered with Roman Numerals, but they don't sort in order, even with 'Natural Sort Order' turned on.
E.g.
Rurouni Kenshin Part III꞉ The Legend Ends
Rurouni Kenshin Part II꞉ Kyoto Inferno
Rurouni Kenshin Part I꞉ Origins

Could the 'Natural Sort Order' option also include Roman Numerals?