unmanaged client somewhere stores wrong IP address of software update server

Using directions from Apple I successfully have had my Yosemite server serve out software updates to unmanaged clients. The server also serves DHCP and DNS and works correctly in all respects, and always has.

Due to circumstances I was forced to change the server's IP address from 192.168.178.201 to 192.168.178.199.

In order to keep serving updates locally, I deleted the preferences on clients as directed per link above, restarted and re-set the prefs file on the client. The preferences read back correctly pointing to 192.168.178.199, also DNS server points to that address (and works).

Since then, launching App Store to obtain software updates, App Store complains , "Didn't get a response from the Software Update server (192.168.178.201)", leading me to believe there is another location where the server's address is kept.

Short of using this dns trick I don't know a solution. Any hints as to where the cause of the aforementioned problem could be found are welcome.