Why IPv6 virtual_ipaddress of keepalived is selected as source?

Issue

• Why IPv6 virtual_ipaddress of keepalived is selected as source?
• How to change it to a NIC's IPv6 address.

Sample configuration:

# nmcli con show ens3 | grep ipv6.addresses
ipv6.addresses:                         2001:db8:0:1::1/64
# cat /etc/keepalived/keepalived.conf
vrrp_instance TEST {
    state MASTER
    interface ens3
    virtual_router_id 1
    virtual_ipaddress {
        2001:db8:0:1::100/64 dev ens3
    }
}
# ip -6 addr show dev ens3
2: ens3: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 2001:db8:0:1::100/64 scope global nodad 
       valid_lft forever preferred_lft forever
    inet6 2001:db8:0:1::1/64 scope global tentative noprefixroute dadfailed 
       valid_lft forever preferred_lft forever
    inet6 fe80::ea7e:d3bc:7601:8eb6/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever
# 
# telnet 2001:db8:0:1::2
Trying 2001:db8:0:1::2...
telnet: connect to address 2001:db8:0:1::2: Connection refused
# 

On another terminal
# tcpdump -i ens3 -nn port 23 2> /dev/null 
15:56:14.450567 IP6 2001:db8:0:1::100.55836 > 2001:db8:0:1::2.23: Flags [S], seq 3490211945, win 28800, options [mss 1440,sackOK,TS val 1176158 ecr 0,nop,wscale 7], length 0
15:56:14.450986 IP6 2001:db8:0:1::2.23 > 2001:db8:0:1::100.55836: Flags [R.], seq 0, ack 3490211946, win 0, length 0
#