BTW, Even with so many firmwares, they cannot even fix an IPv6 problem in about 1.5 years! What's worst? It used to be working! I am not sure what are those engineers focused at.
IPv6 is currently like voodoo. It sometimes work, it sometimes don't. A large portion of the blame lies on the shoulders of ISPs, who are having trouble properly implementing it in a sane way.
You won't find better luck with other manufacturer's routers either. Netgear here is also having different issues (mentioned in these forums), with different ISPs. Some of them lack a simple, sane firewall, opening your entire LAN to it. Others aren't properly implementing various RFCs related to IPv6. Short of running your own *IX box and dealing yourself with the quirks of your particular ISP, you will have a hard time finding a home gateway from any of the usual manufacturers (Asus/DLink/Netgear/TPLink) that works correctly with all ISPs... I suspect that even a business-class Cisco might be problematic if your ISP's implementation isn't "Cisco-friendly".
IPv6, in general, is a huge technological mess. It worries me about the future of the Internet. The fact that after over 10 years it's still not widespread is sign enough on how bad things are with this technology...