there are many abbreviations that do not separate the individual letters (EG: TV, DVD, LCD)
Most spell checkers simply assume it's an abbreviation when only capital letters are used.
So if you need a word to be fully capitalized then you should first type it normally and after that use you word processor's capitalization function. (It's how I do it)
addendum: the mistyping could also produce a (perhaps non-standard) roman numeral.