OK, I was on the phone with Apple Care for two hours. They finally figured out that a folder in my preferences was corrupt. i can't even begin to tell you how he fixed it. But, we did not have to do a clean install and he was able to save most of my preferences. Only my basic preferences had to be redone by me going through all the settings in my system preferences. Sorry I don't have a better answer for you. No clue how this happened, other than it was caused by my upgrade to ML. You are right that if you go in and set up a new user, everything worked perfect. Luckily he was able to save all my other preferences like my Docs, Music, Pics, etc...
Good luck and I hate to say that you should do a backup and maybe to a clean install and then copy all your files back in.
jkk