SQL Server 2012 "Evaluation period has expired" Message After Upgrading to Licensed Edition

I have a old dev box that I run evaluation edition of SQL Server 2012 that I have decided to upgrade to licensed edition. The upgrade went successfully without any issue. However I got below error message after the upgrade when I tried to launch SQL Server Management Studio:

After some Googling or Binging, I found below KB on similar error.

http://support.microsoft.com/kb/971268

However it is for SQL 2008 evaluation edition. Since it is just a old dev box, why not just give it a shot to see what happen. So I just follow "Option 2" but with different path on the registry as this is SQL 2012. Below is the screen shot on what I changed. After that just rerun the upgrade.

Guess what, it works!

If you have similar problem, you might want to try the same thing but try at your own risk especially if it is on production server as this involved registry chance. But why do you run evaluation edition on production server? This supposed to be on SQL 2008 according to the KB, I am no sure why it is happening on my SQL 2012 instance, let me know if you know why.