honestly, i feel the same way. i think its cause even though she gets undressed / naked, they didnt go out of their way to over-sexualize the situations. Like when she was sitting in the sink trying to bathe, or when she was changing clothes in the room.
Now, i wont say that i dont occasionally enjoy the average loli fanservice, but... i dunno, cant quite place it. I think it might have to do how her face is more rounded out, more childish, than the random 'sexy' lolis depicted in other recent anime.
tl,dr: Murasaki isnt sexy, she's just cute. Stop being pedo.