tlstunnel is IPv4-only right now. Extending this to support IPv6 doesn't look like a major undertaking.
(adding blocks to 2672 - the generic IPv6 bug. I added a new bug so whoever gets assigned with solving 2672 doesn't have to investigate whether support is there or not for this component)
Mind bug 4580 when doing this one.
Fixed in r28482.
Verified using build 4289. Both tlwebadm and tlwebaccess (login form)