IPv6 privacy extensions only seam to work at boot with a RTC

[Asmod4n]

When you get a IPv6 Address at boot and have ipv6 privacy extensions enabled like this

cat /etc/sysctl.d/40-ipv6.conf 
net.ipv6.conf.all.use_tempaddr = 2
net.ipv6.conf.default.use_tempaddr = 2
net.ipv6.conf.eth0.use_tempaddr = 2

the "private" addresses get removed when ntpd changes the time to the current time and /proc/sys/net/ipv6/conf/eth0/use_tempaddr gets set to -1 instead of 2.

Here is the dmesg output

[   10.085200] IPv6: ipv6_create_tempaddr: regeneration time exceeded - disabled temporary address support

[popcornmix]

Might be worth reporting this upstream - hard to imagine this is a Pi specific issue.