When IPv6 address to interface is configured and entered in expandend format (e.g. 2001:db8:0:0:0:0:0:1/64) it is not converted to compact format while kernel does that. Once the address is configured it is no longer removable (will be removed from confiuration / config boot, but not from interface)
Lets add expanded format address:
```
# set interfaces ethernet eth1 address 2001:db8:0:0:0:0:0:1/64
# commit
~$ show interfaces
Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down
Interface IP Address S/L Description
--------- ---------- --- -----------
eth1 2001:db8::1/64 u/u
~$ cat /config/config.boot
ethernet eth1 {
address 2001:db8:0:0:0:0:0:1/64
...
}
```
And now delete it:
```
# delete interfaces ethernet eth1 address
Possible completions:
2001:db8:0:0:0:0:0:1/64
# delete interfaces ethernet eth1 address 2001:db8:0:0:0:0:0:1/64
[edit]
# compare
[edit interfaces ethernet eth1]
-address 2001:db8:0:0:0:0:0:1/64
[edit]
# commit
# exit
```
Removed from configuration but not from interface:
```
~$ show interfaces
Codes: S - State, L - Link, u - Up, D - Down, A - Admin Down
Interface IP Address S/L Description
--------- ---------- --- -----------
eth0 46.13.3.219/28 u/u
eth1 2001:db8::1/64 u/u
eth2 100.82.20.66/22 u/u
ifb0 - u/u Ingress for eth0
lo 127.0.0.1/8 u/u Loopback
::1/128
vtun0 172.16.4.129/29 u/u
~$ ip a dev eth1
Command "dev" is unknown, try "ip addr help".
~$ ip a li dev eth1
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 00:50:56:b2:88:1a brd ff:ff:ff:ff:ff:ff
inet6 2001:db8::1/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::250:56ff:feb2:881a/64 scope link
valid_lft forever preferred_lft forever
```