ok found it. I have no dhcp server with IPV6, I was sure of that, it is the IPv6 of my router
eth0 Link encap:Ethernet HWaddr F8:1A:67:51:67:7C
inet6 addr: fe80::fa1a:67ff:fe51:677c/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:213960 errors:0 dropped:0 overruns:0 frame:0
TX packets:169085 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:211886797 (202.0 MiB) TX bytes:84452425 (80.5 MiB)
What I discovered tonight it is that all servers (even NS6 and NS7) get an IPV6, but my router (openwrt) answers its ipv6 (however no activated dhcp server on IPV6). When I set the ipv6 settings of anaconda to 'ignore' (--noipv6), I have no problem of bad IPV6 dns entry.
does the --noipv6 can be tricked by kickstart as a default setting ?