"disable_ipv6 == 1" on VLAN interfaces

Hi, I am trying to figure out how to make IPv6 work and noticed that ipv6 is disabled by default on all VLAN interfaces: is that normal?

sysctl -a 2>&1 | egrep "eth.*disable_ipv6"
net.ipv6.conf.eth0.disable_ipv6 = 0
net.ipv6.conf.eth0.2.disable_ipv6 = 1
net.ipv6.conf.eth1.disable_ipv6 = 0
net.ipv6.conf.eth1.1.disable_ipv6 = 1
net.ipv6.conf.eth1.11.disable_ipv6 = 1
net.ipv6.conf.eth1.22.disable_ipv6 = 1
net.ipv6.conf.eth1.33.disable_ipv6 = 1

The default is that IPv6 works.
In my router every subinterface has disable=0, however I never touched anything there.