Comment 11 for bug 254622

Clerum, for me it works under 8.10 (Kubuntu) actually.

The problem exists only after bringing up the interface, e.g., ifdown eth0 followed by
ifup eth0 results in ip -6 r s default
default via xyz dev eth0 proto kernel metric 1024 expires 527sec mtu 1280 advmss 1440 hoplimit 64
but removing the default route
ip -6 r del default
and waiting some seconds on the unsolicited router advertisements (announcing 1280 due
to IPv6 tunnel) re-adds the default route correctly.
ip -6 r s default
default via xyz dev eth0 proto kernel metric 1024 expires 538sec mtu 1280 advmss 1220 hoplimit 64
 I use this as a workaround. Furthermore, the problem didn't exist in the same kernel version under debian, so it seemed to be ubuntu specific.