Comment 2 for bug 1533631

Yes, seeing this too on 15.10 since around the first week of March, as best I can tell, but irrespective of Suspend.

It looks like dhclient thinks/is told the new lease is 'depreferred' and therefore quits, and the dhclient process is terminated, but the address remains on the interface until the valid-lifetime expires.

Mar 22 16:06:02 hephaestion NetworkManager[1468]: <info> Activation (wlp3s0) Beginning DHCPv6 transaction (timeout in 45 seconds)
Mar 22 16:06:02 hephaestion NetworkManager[1468]: <info> dhclient started with pid 19221
Mar 22 16:06:03 hephaestion dhclient: XMT: Confirm on wlp3s0, interval 950ms.
Mar 22 16:06:03 hephaestion dhclient: RCV: Reply message on wlp3s0 from fe80::ee43:f6ff:fe46:c080.
Mar 22 16:06:03 hephaestion dhclient: message status code Success.
Mar 22 16:06:03 hephaestion NetworkManager[1468]: <info> valid_lft 86400
Mar 22 16:06:03 hephaestion NetworkManager[1468]: <info> preferred_lft 86400
Mar 22 16:06:03 hephaestion dhclient: PRC: Rebinding lease on wlp3s0.
Mar 22 16:06:03 hephaestion NetworkManager[1468]: <info> address 2a02:8011:2007::2
Mar 22 16:06:03 hephaestion NetworkManager[1468]: <info> nameserver '2a02:8010:1:0:212:23:3:100'
Mar 22 16:06:03 hephaestion NetworkManager[1468]: <info> (wlp3s0): DHCPv6 state changed unknown -> bound
Mar 22 16:06:03 hephaestion NetworkManager[1468]: <info> Policy set 'wireless.lan.iam.tj' (wlp3s0) as default for IPv6 routing and DNS.
Mar 22 16:06:03 hephaestion NetworkManager[1468]: <info> Writing DNS information to /sbin/resolvconf
Mar 22 16:06:03 hephaestion dnsmasq[2433]: setting upstream servers from DBus
Mar 22 16:06:03 hephaestion dnsmasq[2433]: using nameserver 2a02:8010:1:0:212:23:3:100#53
Mar 22 16:06:03 hephaestion dnsmasq[2433]: using nameserver 10.254.1.254#53
Mar 22 16:06:03 hephaestion nm-dispatcher: Dispatching action 'dhcp6-change' for wlp3s0
Mar 22 16:06:03 hephaestion dhclient: PRC: Address 2a02:8011:2007::2 depreferred.
Mar 22 16:06:03 hephaestion NetworkManager[1468]: <info> (wlp3s0): DHCPv6 state changed bound -> unknown
Mar 22 16:06:03 hephaestion NetworkManager[1468]: <info> (wlp3s0): DHCPv6 state changed unknown -> expire
Mar 22 16:06:03 hephaestion NetworkManager[1468]: <info> (wlp3s0): canceled DHCP transaction, DHCP client pid 19221
Mar 22 16:06:03 hephaestion NetworkManager[1468]: <info> (wlp3s0): DHCPv6 state changed expire -> done

$ ip -6 addr show dev wlp3s0
3: wlp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 state UP qlen 1000
    inet6 2a02:8011:2007::2/128 scope global dynamic
       valid_lft 82942sec preferred_lft 82942sec
    inet6 fe80::21f:3bff:febd:7485/64 scope link
       valid_lft forever preferred_lft forever