Re: how long has this bug been around?
Web server? I should hope so. It's usually just a case of enabling it in Apache etc.
Your home? Probably not. Virgin haven't even tried to deploy IPv6 to normal homes yet, despite being DOCSIS 3 which mandates compatibility with it.
Wifi hotspot? See above.
3G/4G? IPv6 is mandated as part of those protocols. Probably more phones use it than they do IPv4 when connected direct to the cell network, rather than wireless.
I have an IPv6 website, email, etc. server. It's not a huge majority of traffic, but its definitely "there" and been working fine for years. Google servers prefer IPv6, for instance, so almost all GMail and Google traffic use it first, and I get IPv6 mail from Google all the time.
It's certainly not "untested". Hell, IPv4 was still finding problems DECADES after deployment (ping-of-death, Xmas-tree packets, ECN, you name it). But to suggest it should be "bug-free" even 20 years from now would be moronically stupid for such a thing.