IPv6 and Prefix Delegation from ISP __ Is that normal?

An OpenWRT router receives its IPv6 settings via dhcpv6 and

ifstatus wan6

gives

"ipv6-address": 
       "address": "2406:13a2:0:2:6013:6aa5:803:7ca4",
       "mask": 128,

"ipv6-prefix":
       "address": "2406:13a2:19b:2400::",
       "mask": 56,
       "class": "wan6",
       "assigned": 
            "lan": {
                "address": "2406:13a2:19b:2400::",
                "mask": 60 }

Comparing the address and the prefix

2406:13a2:0000:0002:6013:6aa5:803:7ca4
2406:13a2:019b:2400::

Shouldn’t the first 56 bits of the router IP and the PD be the same?

Note: these settings were confirmed after upgrading Openwrt and reset of the whole configuration.