Device connected to local network with IPv6 despite noipv6 setting

In dhcpconf.conf file I have set noipv6 in the section of interface used for the connection, in past this apparently worked, now the device has assigned both IPv4 and IPv6 as I can se from inet6 address in ifconfig output, and if I try to connect to it from another device in the network using IPv6, it connects correctly with the IPv6 assigned normally. How I can make sure only IPv4 is assigned?