I just purchased a nice Gitzo GH1780QR ball head for my tripod. This head has a nice set of 3 levels that make it easy to properly level the camera. I have been using my Canon 100-400mm lens with it. I've noticed something odd about the way this lens particular mounts onto my camera when I bolt the Gitzo head plate to the lens rather than the camera body. When set perfectly level, the camera body itself appears to be tilted a few degrees, so when taking a shot, it is not fully horizontal. I am using a Canon Rebel XSi (450D) body.
Is this something normal and expected with the EF 100-400mm IS USM L lens from Canon? Or is this a defect, and something I should have fixed? To resolve the imbalance, I have to tilt the ball-head slightly off-axis, but this in turn affects panning.