For the record, Mihawk did something similar to me when we were fighting the other day. I swear, his spaz bullets clipped right through the corner of a building and killed me. I attempted to recreate it by fighting against him again, but as soon as I mentioned something about it to him, he immediately quit with a spree of 10, which I also thought was suspicious. I didn't pursue a ban against him because I didn't feel confident enough that it was a hack, but now that somebody else has mentioned it, I think it's worth a second look.
Incidentally I hear he's been banned in the past, for what I'm not sure. I'll wait to see what other admins have to say.