resolve problem in particular environment

[sk.flyr]

Hello,

I can resolve ok.example.org in the environment.
also I can resolve www.example.org and ipv6.example.org.
I cannot resolve ng.example.org in the environment.
Is it normal?

dual stack environment
 ipv4 - configure pppoe on windows(vista,7,8) adopter
 ipv6 - received RA on Ethernet

DNS records
 ok.example.org. CNAME www.example.org.
 www.example.org. A 192.0.2.80
 www.example.org. AAAA 2001:db8::80
 ;
 ng.example.org. CNAME ipv6.example.org.
 ipv6.example.org. AAAA 2001:db8::80

-- 
flyr