If you "ignore" a person, you don't have anything to do with that person but their free choice of whether to have anything to do with you is still there. They do not know if you have ignored them, that's for your purposes, not theirs. If I did not want to hear/see someone's posts I'd send them a polite PM and ask them not to comment on my threads or page, wait a bit to see if I got a reply, and then I would ignore them. You cannot blame a person for posting on your page after you have ignored them; they don't know; you are the one with a problem with them, they may not have a problem with you.