Those dogs do not have agro, you need to pick one, not run away and just dps it down. The boss also carbonites the tank and drops agro every ten seconds or so.
90% of the time when im tanking I kill the boss before the dps even kill the adds cause they are running all over the place like chickens with their heads cut off losing dps on the adds. The dogs don't do much dmg as long as they don't get in the red circle around the boss.
I was surprised the first two times this happened, but it has become pretty normal for me as well. Seeing them run in fear at times can be quite hilarious, though.