Outlook 2013 opening extra Office 365 / Exchange account - cannot close

I'm running Outlook 2013 on Windows 8 and have an odd problem. When I setup my account on any computer or create a new Outlook profile with just my account, it opens another account as well. The other account shows up in my folders list and gets synced along with everything else.

At one time I needed access to this additional account and had added the account under the open additional mailboxes setting in Outlook on one of my computers. I no longer need access to it, so removed it from the settings, but it Outlook still opens it. If I right click the mailboxes folder and click close, it tells me to remove it from account settings, but it is no longer there.

Now the odd part to me is that if I setup a new Outlook profile on any computer, the extra account shows up there as well after a little while. Again no reference to it in account settings and again it won't allow me to close the folder.

I'm guessing this must be something related to settings being synched in Office 365 or Windows 8, but I can't seem to find it and I can't seem to stop this account from showing up on my computers.

Thanks for any ideas