samba - Apr 2012 - Samba 3.5.12 Rejects Connection via NetBIOS Name for Out-Of-Workgroup Clients

All,

I have been using samba 3 in a production environment for about four 
years, authenticating via ADS against a Windows SBS 2008 server.  I've 
never had any trouble connecting via the NetBIOS name or the DNS, until 
quite recently.

Now, attempts to connect via the NetBIOS name (\\server) fail, and 
generate errors like these:

    [2012/04/25 13:55:00.970428,  1]
    smbd/sesssetup.c:332(reply_spnego_kerberos)
       Failed to verify incoming ticket with error NT_STATUS_LOGON_FAILURE!

These errors occur almost alternately in the "log.client_name" or the 
"log.client_ip" files.

Connections via the DNS name (\\server.domain.tld) connect correctly and 
do not generate any errors.

Why would authentication be failing via the NetBIOS name?

Thanks in advance,

-Andy