nslookup problem

[Bind]

Hi
I have an authorative dns server which handle my domains.
also my dns server is a recursive. so i set it in my hosts.
when i run nslookup on a windows machine and do a query about domains which 
my dns server isnt authorative about them like yahoo.com it returns:

Non-authoritative answer:
Name:    yahoo.com
Addresses:  72.30.2.43
          98.137.149.56
          209.191.122.70
          67.195.160.76
          69.147.125.65m
ok,my server isnt authorative about yahoo.com and everything is correct.but 
when i ask about domains which my dns server is authorative about them it 
returns the same structure(Non-authoritative answer:):
> www.report.dci.ir
Server:  [217.218.127.105]
Address:  217.218.127.105

Non-authoritative answer:
Name:    www.report.dci.ir
Address:  217.218.127.123

why? since my dns server is authorative about dci.ir and i think it show 
"authorative answer"!
what is the reason?
thx
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