A few other words do it too (rot13("znfgheongvba") does it as well, but only some of the time). I don't think this is caused by a hard-coded blacklist of words, but I'm not really sure exactly what conditions have to be met for it to happen.

@scarecrowbob: Your comment (the one that is a sibling to this comment) is also [dead]. I have no idea why, this is getting kind of absurd...