I agree with John - it's likely your collimation is off.
What eyepieces are you using in both the 12" and the refractor?
Can you describe some of the differences you see between them both?
We're having a new-moon meet up at Mangrove Mountain on Saturday night - you're more than welcome to come up and join us. Bring your 12" dob and I'll happily check/adjust the collimation for you if it's out. It's also significantly darker there than the 'burbs, so you'll be able to see a lot more too. Check the star parties forum for a map and other details.
Hope to see you there,

to IceInSpace!