Ok I figured it out, as always pilot error, sort of. Turns out my wasd key bindings were messed up, so translate and roll were activating together. I must have changed one and forgot to change the other at some point.
So I built an Orbital fuel depot, just a simple big tank really, but when I attempt to dock/undock with it, my RCS can't translate laterally. It translates vertically, and longitudinally, but not laterally. The thrusters are all balanced. It goes up, down, forward, and backward straight, but when I try to move laterally it just spins along its longitudinal axis. Changing modes affects the other movements properly but it seems like roll is stuck in rotational mode. Anybody have a similar issue?