This is a bug for icon-naming-utils.
When you "mount" a connection to a smb server in Nautius (using File->Connect to
Server..), the icon that will appear on desktop will use the icon
See also this on nautilus devel list
Created attachment 4280 [details] [review]
The proposed patch
Fixed in CVS.
You missed the other two smb MIME type icons btw. There's also one for
workgroup, and one for server. :) Thanks for the bug report.