Outlook unaware of mailbox migration

Hi

We are migrating mailboxes from E2007 to E2013 and most of the time users correctly receive the prompt:

The Microsoft Exchange Administrator has made a change that requires you quit and restart Outlook

However, in some cases users do not receive this. Outlook shows "connected" but they are not actually connected

The PublicFolderDatabase value is the same in both environments as we only have 1 in 2007:

Output from E2007 database:

Get-MailboxDatabase "E2007DB" | fl *pub*
PublicFolderDatabase           : Server\Public Folder Database\DB1

Output from E2013 database:

Get-MailboxDatabase | fl *pub*
PublicFolderDatabase   : Server\Public Folder Database\DB1

If I remove the value from the E2013 servers, will that force a prompt for all clients?

Thanks

shapi