So I launched a space station core in orbit around Kerbin. It's made up of (from top to bottom) a Cuppola module with 4 high gain antennae, a hitchhiker with 4 docking ports mounted around it, a service bay holding batteries, a RSC fuel tank, a Liquid-Oxidizer fuel tank with RCS controllers and 8 OX-4L around it and a poodle engine at the end. I had no problem getting it into space and achieving a stable orbit have since had it docked with with a laboratory, lander I needed to refuel before sending to Mun, and another fuel tanker I sent up to refuel the station. I'm planning on moving the think to a Munar orbit so dedocked the lab and started my burn only to find that after 3 - 5 seconds it started pitching and will spin uncontrollably if I don't turn the engine off. From what I can tell there's nothing that should be unbalancing it. I also tried filling the tank to full thinking maybe it's top heavy (it was at half tank), but that didn't do anything either. Is there something I'm missing? The only thing I can think is that it's unbalanced, but for the life of me I don't know how.