I wouldn't say it's a bug, it's probably just a design flaw. Maybe the devs thought that if you hit with a fire spell, a character with retribution would "splash the fire back", and since that creature heals with fire, it'd heal by hitting you. It makes sense, but on the mechanical level, it makes the build unfeasible (at least on a solo gameplay), specially because it's not something you can deactivate: it means you're spending combat points that actually work in favor of your enemy.
I'm willing to test this build on the tactician mode when the game is released, but I'll be frustrated if it works like this. Maybe that's the price you pay for being a one-trick-pony.
