As far as I know, the bug does not exist in Windows 7 or vista.
The bug is not seem in ethernet IPv6 native enviroment(without pppoe).
When connected to ipv6 enabled pppoe server, windows use IPv6 Control Protocol to negotiate interface identifier(link-local address).
Then Windows send IPv6 ICMPv6 Router Soliciation(RS). PPPoE server reply Router Advertisement(RA).
In RA, there are flags such as [Managed address configuration],[Other configuration] which indicate to use dhcpv6 to negotiate address and/or other configuration such as DNS server and so on.
We can use netsh int show interface [broadband connection interface id number] to show Broadband Connection Parameters.
We can find items [Managed Address Configuration] and [Other Stateful Configuration] in parameters list.
In windows 7, these Managed/other parameters in netsh is the same with RA packet.
In Windows 8.1, the M/O parameters in netsh is always enabled when in a IPv6 enabled PPPoE connection.
The bug will cause Windows 8.1 DHCPv6 client insist asking DHCPv6 server for IPv6 address.
In M=0,O=1,PPPoE enviroment, Windows 8.1 client keep sending DHCPv6 Solicit packet with [Identity Association for Non-temporary Address] requirement. DHCPv6 server which have no address to allocate will reply DHCPv6 Advertise with status code fail[1]. Windows 8.1 sometimes send DHCPv6 Information-request without asking for Non-temporary address. DHCPv6 server can reply other configuration and status code success[0].
In M=0,O=1,PPPoE enviroment, windows 7 only send DHCPv6 Information-request, not send DHCPv6 Solicit.
If someone want to manual change M,O flags in netsh, [Router Discovery] flag should be disable first.
Windows 8.1 IPv6 RA M,O flag =1 in PPPoE connection problem is a BUG or FEATURE?
BTW, When RA M=1,O=1 in PPPoE, Windows 8.1/7 still can NOT connect to network. I post the detail here:
http://social.technet.microsoft.com/Forums/windows/en-US/566d95aa-ffe7-40d8-9a57-6f4ebaa0d82f/ipv6-address-obtained-from-dhcpv6-in-pppoe-does-not-work-in-windows-7-and-8?forum=w7itpronetworking