The way that it works here is that as long as you don't have the Guest network on when you reboot, IPv6 is fine. You can turn the Guest network off, and reboot, and IPv6 is fine. And then you can turn the Guest network back on after rebooting with it off, and IPv6 keeps working.
So if you lose IPv6 because you rebooted with the Guest network on, it's faifly easy to recover. As long as you know that.
I agree that there should be release notes with every firmware release so tha tpeople don't waste time figuring out what Linksys already knows.