How to stop Outlook from autocorrecting double capitals at the beginning of some (but not all) words?

I commonly use words that start with double capitals - for example, I have a lot of research assistants (commonly referred to as "RAs").  However, "RAs" continuously autocorrects to "Ras," no matter how many times I change it back.  And I have to make sure I type a word after the autocorrected term, then go back and change it (if I change it before typing a new word, it will autocorrect again when I press the spacebar).

I've tried teaching it to the dictionary, but can't figure out how - it doesn't register as a misspelled word, just one with incorrect capitalization...so I can't use the "show spelling and grammar" submenu to teach the program new terms.

Does anyone have any ideas for how to fix this, other than disabling the "autocorrect double capitals at the beginning of words" feature for ALL words?

Thanks!

Adrian