Getting an unusual IPv6 address on a IPv4 only wwan interface

Ahoi,

I got a LTE card here which I configure using modemmanager cli. Sadly it only has IPv4 connectivity and I have to set the IP address manually. This all works pretty nicely. What is a bit strange, is that the interface always gets an additional IPv6 address. Which causes my system to think that it has IPv6 connectivity and tries to resolve stuff by IPv6. This is extremely annoying and so far I couldn't figure out where this IPv6 address is coming from.

The address in question can be seen here:

$ ip address show wwp0s20f0u6 34: wwp0s20f0u6: <BROADCAST,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UNKNOWN group default qlen 1000 link/ether my:ma:ca:dd:re:ss brd ff:ff:ff:ff:ff:ff inet 10.32.555.333/16 brd 10.32.255.255 scope global wwp0s20f0u6 valid_lft forever preferred_lft forever inet6 ::fc11:myma:cadd:ress/64 scope global mngtmpaddr noprefixroute valid_lft forever preferred_lft forever inet6 fe80::fc11:myma:cadd:ress/64 scope link valid_lft forever preferred_lft forever

It's this one: inet6 ::fc11:myma:cadd:ress/64 scope global mngtmpaddr noprefixroute

The address configuration is done by systemd-networkd and configures only a static IPv4 address.

Does someone have a clue where this IPv6 address comes from?