Welcome to the forums. Thanks for posting and thanks for doing a little searching to fix your problem. Its an installer bug as the credentials are set correctly on liveCD to sudo, but revert to su upon install. I have not had time to get to the root cause, but I know that its annoying.
Thanks for sticking with it. I appreciate you joining up and giving it a spin.
We have old and new forums as we are transitioning..So lots of info in the old ones that are not directly applicable in many cases, but have a good bit of general linux knowledge in them also. We are trying to build up the new forums now that we have switched to Debian.
Thanks much and enjoy...biff