Ahri Charm (E) not cancelling Warwick Ulti?

I just played a ranked game and was aggravated bc i died about three times because i could not self-cancel warwick ulti and i think it is a bug because I'm sure charm doesn't wear off when I'm silenced. I would charm when he ran to ult but it hit when he went to me but he was just hacking at me while having the charm active on me. i didn't record so I'm not sure if i was consistently hitting him before he came and he ulted through it or i hit it when he ulted but I'm convinced it hit when he was on me.