Duplicate IPv6 address

/etc/config/network configuration

config interface'lan'
option type'bridge'
option ifname'eth0.1'
option proto'static'
option delegate '0'
option force_link '0'
option ip6assign '60'
option ip6ifaceid'::100:20'

/etc/config/dhcp configuration

config dhcp'lan'
option interface'lan'
option force '1'
option ra'server'

Only the route advertisement is turned on, but DHCPv6 is not turned on

ifconfig -a command result

    inet6 addr: 240e:346:***::100:20/60 Scope:Global
    inet6 addr: 240e:346:***::100:20/60 Scope:Global

Here is PPPoE dial-up. Why does show two identical inet6 addrs? What's more strange is that another machine with the same configuration shows that there is really only one address. Does this have anything to do with the operator?