Wow, I just had to post something after I read Outlook's MVP CONDESCENDING reply to a simple question by a user. I found this because I too recently came up with the same problem. Forget that it's 3 years after the first post. As is typical with all of Microsoft junk, I had to figure out a work-around for this issue (spending countless wasted time), because it just does not work the way it should. You can try one of two ways... you can "Import" the second account (file, import-export), or "Add" the Data File (tools, options, mail setup, data files), but leave the first Data File in place, and keep it as the default file. You should now have two Data Files available, and the "Contacts" should now be visible (even if it's not the default). It worked for me.
Take that you MVP jerk!!