We just migrated our SBS 2003 server to server 2012 R2.
Our SBS 2003 server previously ran exchange and it was removed, however when we installed server 2012 and migrated from google apps to exchange we saw some legacy mailboxes. We removed said mailboxes and recovered the active directory accounts/profiles by restoring the tombstones.
We've been noticing some weird things that we've been fixing, but this one is stumping us and is a bit crazy.
So far we've found one user who can logon to OWA using a blank password. Their normal password will work as well when logging in, however any password that isn't just blank, and isn't their password will result in a incorrect password error when trying to logon.