Krish Gali posted about a change that is planned to happen in Office365 to support the new groups experience. The groups that we have Today as All Groups will be renamed to All Distribution Groups.
We announced earlier this year that we’re introducing a new Groups experience that will unify people, conversations, and content across Exchange, SharePoint, and Yammer. You can read more about Groups in the Evolution of email blog post. To prepare for the introduction of Groups, we are changing how some of the address lists are organized in Exchange Online.
Read more at source:http://blogs.office.com/2014/05/16/changes-to-default-address-lists-in-exchange-online/