Ping of a link local address with -I as non-root produces "Invalid argument"

iputils-ping 3:20161105-1ubuntu2 amd64 18.04.1 LTS

In the following, "c7" is a host with the link-local address fe80::5054:ff:fe45:1e87.
The mapping is in "/etc/hosts". It is reachable via the "enp2s0" interface on the local
machine. I have masked the local machine's MAC address.

1. As a regular (non-root) user, ping returns "Invalid argument":

$ ping -I enp2s0 c7
PING c7(c7 (fe80::5054:ff:fe45:1e87)) from fe80::xxxx:xxff:fexx:xxxx%enp2s0 enp2s0: 56 data bytes
ping: sendmsg: Invalid argument
ping: sendmsg: Invalid argument
ping: sendmsg: Invalid argument

2. As root, ping works:

# ping -I enp2s0 c7
PING c7(c7 (fe80::5054:ff:fe45:1e87)) from fe80::xxxx:xxff:fexx:xxxx%enp2s0 enp2s0: 56 data bytes
64 bytes from c7 (fe80::5054:ff:fe45:1e87%enp2s0): icmp_seq=1 ttl=64 time=0.285 ms
64 bytes from c7 (fe80::5054:ff:fe45:1e87%enp2s0): icmp_seq=2 ttl=64 time=0.306 ms
64 bytes from c7 (fe80::5054:ff:fe45:1e87%enp2s0): icmp_seq=3 ttl=64 time=0.307 ms

3. Specifying the interface-qualified IPv6 address directly works:

$ ping fe80::5054:ff:fe45:1e87%enp2s0
PING fe80::5054:ff:fe45:1e87%enp2s0(fe80::5054:ff:fe45:1e87%enp2s0) 56 data bytes
64 bytes from fe80::5054:ff:fe45:1e87%enp2s0: icmp_seq=1 ttl=64 time=0.476 ms
64 bytes from fe80::5054:ff:fe45:1e87%enp2s0: icmp_seq=2 ttl=64 time=0.408 ms
64 bytes from fe80::5054:ff:fe45:1e87%enp2s0: icmp_seq=3 ttl=64 time=0.395 ms