Negative Rakeback?

There are a bunch of people who insist that it never hurts to get rakeback. But every once in a while, I come across a post where somebody talks about how they got "negative rakeback" when they had a bonus subtracted from a small rakeback amount where they played just enough hands to play off a bonus. I recently read a long thread about how this has happened to many full tilt players, where they actually gave most of a bonus back after it was subtracted from RB. I would like to see some "experts" who call people "idiots for giving up free money" confront some people who claim that they have gotten negative rakeback. The mysterious fact that I never have seen this type of confrontation has made my 5-10 hours of research in here almost entirely worthless. Will a REAL expert please step up? Don't bother explaining how bonuses are worth more at lower limits and RB is more at high limits blah blah blah. WHO actually subtracts negative rakeback from your account and who doesn't? I DON'T want to "make sure that I get RB at every site I join" if it WILL make a difference in bad way when I only plan to play off bonuses in a particular site.