Pretty common from my experience. In all likelihood, the lower mounting tabs are not square (parallel), so when you tighten them down it forces the rack off center. My last OMM was that way and not easy to straighten due to it's design, but the Jandd have a longer mounting arm so take it back off the bike, eyeball it and tweak slightly with a long crescent wrench. You can also bend it straighton the bike but you risk putting a lot of torque on the braze-on - I would probably try the wrench first.