See, if you're addressing something to "MR AND MRS BLANK", MS Word automatically changes it to "MR AND Mrs BLANK".
Typing it the other way around - that is, as "MRS AND MR BLANK" (on the basis that perhaps the word that comes after "and" gets downsized from all caps) - gets you the same result: "Mrs AND MR BLANK". You have to go back and retype the "Mrs" as "MRS" to make it stay that way.
I think it's a sexism in play - albeit in a small way, but irritating to me because I tend to address envelopes to clients with the names and address in all caps as it's easier that way - except for this little hitch.
And did I mention it's sexist?
Disclaimer: There might be some way of turning off this annoying feature, but I for one don't know of it. Ideas, anyone?