It refuses to consistently block a single, inline add on the Youtube home page that masquerades as a video suggestion, one of the worst kinds. Sometimes it will, sometimes it won't. When I re-block it, it is always the same element I'm blocking.

Perhaps it keeps un-blocking it because this ad pretending to not be an ad is considered an 'acceptable ad', but thats rampant speculation.

Don't forget to configure your adblock addons, because the way its configured by default usually benefits them at your expense.