We have a single domain forest and have always been able to add computers with either the full domain name "contoso.priv" or the short name (pre-Windows 2000 name) "CTS". Today, I attempted to add a computer using the short name and it did not work.
Info that might be relevant:
We recently demoted/retired our last server 2003 DC
Domain Functional level is still 2003
While the demotion went very smooth for the most part, we had to clean up a lot entries in the dns module for our old DC.
I'm happy to provide more info if anyone needs it Any help would be greatly appreciated.