i think Chronos was the first to discover it, although it took me awhile to figure out what he meant once when someone asked why he said Mail and he said the game wouldn't let him type her real name.
Mia and i talked with Stormy about it, and we'd worked out that if you typed something like:
a Mail
b Mia
c Lightning
you'd see lines a and c but not b. the only guess we had is that they might not be looking at it as offensive, but as the acronym MIA (Missing In Action). they might not want any of that kind of discussion in game, so they block any line that contains it entirely. i just wish they'd let you know the entire line was blocked, because it doesn't even show up in italic or red.
sail with you later! 
Littlebell