it's an expected behavior, if you do not add your current domain (abc.com) in the AD domain suffix trust
1. Open "Active Directory Domains and Trusts", Add abc.com as an UPN suffix.
2. Change your current all AD users logon name from @abc.local (or whatever you defined) to @abc.com
3. Run the force synchronization in DirSync, or wait for the next synchronization.
You will see the users are synchronized using @abc.com