Perhaps one of the following will help diagnose what is going on with the connection.
use Wireshark to see the difference?
What does the log file say for samba
It is clear that when the NAS joins the domain and makes a DNS entry, it is doing something that corrupts that domain name. I cannot find any distinctions in any listing, so I have no idea what is being done. This may actually be a "Feature" of the NAS for which there is a preference setting.
I have managed to enter several domain names for IP 10.1.1.80 which worked, "C:\> dir <XXX>.TCLC.org\d0" until I named the NAS <XXX> and joined the domain. From that point on, that specific domain name was now corrupted -- even when I changed the name of the NAS and I deleted and re-entered that domain name. It is not clear if there is a less draconian rehabilitation, but deleting all known instances and caches, and re-booting seems to do the trick.
Now that I have a clear mechanism, I should be able to search for similar experiences and/or open a support ticket with ASUS.