We can use words in books, as book titles, and on animals that are completely unfiltered, and yet, we cannot use a long list of words on our house signs, and I believe in other select circumstances as well, including guild titles and guild names. I do not believe that this is a bug, but rather what was meant to be a well-intentioned effort to restrict inappropriate language, however, it was applied without giving the filter itself restraint. As such, you cannot use words like Compassion, Assassin, and many other very valid, and appropriate words. I believe the game's audience is mature enough to restrain themselves, and much like using offensive language in game, there are steps that can be taken to eliminate any trouble-makers. Thank you.