Assume that you deploy Directory Synchronization for Office 365 in a Microsoft Exchange Server 2013 environment. When you use the New Remote Mailbox wizard in Exchange Admin Console (EAC), the organizational unit picker is not available.
This issue occurs because of a logic issue in Exchange Server 2013.
To fix this issue, install cumulative update 10 for Exchange Server 2013.
To work around the issue, use the New-RemoteMailbox cmdlet that contains the OnPremisesOrganizationalUnit parameter to create remote mailboxes.
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.