I agree. This is something I can't be prescriptive about any more, especially since I usually say "None of them have ..." There's probably a subtle difference depending on whether the emphasis is singular or plural.
"None of them has bothered to pick up the newspaper!" Here, I'm annoyed that not even one of them has done it.
"None of them have seen the movie yet." Here, I'm commenting that they all haven't seen it.
There are contextual issues that might nudge you in one direction or another without being aware of it.