are these actually responding on ipv6 or are they resolving ipv6. If they are resolving to IPv6 they might be cached or have ipv6 addresses registered in DNS.
I’d try (at the command prompt) running:
ipconfig /flushdns nbtstat -R
then seeing if you have the same problem
i had a similar problem and i’ve disabled ipv6 by following this http://support.microsoft.com/kb/929852
in short create a DWORD entry named
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip6\Parameters\ and give it the value0xffffffff
if you want to ping prefer by IPv4 over IPv6 following this http://support.microsoft.com/kb/929852/en-us and get fix it tool (Prefer IPv4 over IPv6 in prefix policies)
It’s work for me.