Default Address Book is changing from GAL to an Address List

I have an Exchange 2010 server.  Clients are a mix of Outlook 2007 and Outlook 2013.  Server has been in place for a few years now.  When the server was installed, I created individual Address Lists based on locales.  Up until several weeks ago, the default Address Book has been the GAL.  Now, the default Address Book for some users has changed from the GAL to one of my created Address Lists.  I can manually change it back per user by going into the Outlook Address Book settings.  

What would have caused this to happen and how can I change the default back for all users without going to each workstation one by one?
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

Raymond PengSystems EngineerCommented:
No existing GPO to do this.

This would need to be  accomplished by creating and modifying a new GAL. The steps can be found below.

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today

From novice to tech pro — start learning today.