I stumbled across http://en.wikipedia.org/wiki/Hentaigana while reading the article about that IME thing.
From it:
> Note that this hentai (•Ï‘Ì: "variants") is not the same word as the hentai (•Ï‘Ô) from which the English slang term is derived.
More evidence that hentai can mean different things, I guess.