An update to my earlier post on this problem: if you have a Mac running OS X Server 10.5.8 or 10.6 and it has more than one network connection to a subnet, it will see itself when it checks for other servers with the same serial number.
Apple has fixed it for 10.5.8 and 10.6.
http://discussions.apple.com/thread.jspa?messageID=10396995#10396995
Apple fixed this problem in the “Mac OS X Server 10.5.8 Update v.1.1”.
<http://support.apple.com/downloads/Mac_OS_X_Server_10_5_8_Update_v_1_1>
The “Network Registration Update” for 10.6 fixes it.
<http://www.apple.com/downloads/macosx/apple/macosx_updates/networkregistrationupdate10.html>
The 10.6.1 update contains the fix as well.
details here: <http://www.apple.com/downloads/macosx/apple/macosx_updates/macosxserverv1061update.html>