This bug has not been tagged before as 'wily' and unfortunately I have created a duplicate bug report of this one, not being able to find it earlier.

A few more observations from my original bug report:

It looks like the network is not up when the mounting is done however systemd dependencies as well as unit files generated from /etc/fstab seem to be OK

$ tail -2 /etc/fstab
# Media Library
disk.lan:/volume1/Library /media/Library nfs rw,async,auto,nfsvers=3 0 0

$ systemd-analyze dot media-Library.mount
digraph systemd {
        "remote-fs.target"->"media-Library.mount" [color="green"];
        "remote-fs.target"->"media-Library.mount" [color="black"];
        "media-Library.mount"->"network-online.target" [color="green"];
        "media-Library.mount"->"remote-fs-pre.target" [color="green"];
        "media-Library.mount"->"systemd-journald.socket" [color="green"];
        "media-Library.mount"->"system.slice" [color="green"];
        "media-Library.mount"->"network.target" [color="green"];
        "media-Library.mount"->"-.mount" [color="green"];
        "media-Library.mount"->"-.mount" [color="black"];
        "media-Library.mount"->"system.slice" [color="grey66"];
        "media-Library.mount"->"network-online.target" [color="grey66"];
        "media-Library.mount"->"umount.target" [color="red"];
        "umount.target"->"media-Library.mount" [color="green"];
        "umount.target"->"media-Library.mount" [color="red"];
}
   Color legend: black = Requires
                 dark blue = Requisite
                 dark grey = Wants
                 red = Conflicts
                 green = After

Despite the correct dependency between "media-Library.mount" and the "network-online.target" looking at the journal log reveals that the network is not yet started when the "network-online.target" is reached.

$ journalctl --boot _COMM=systemd _COMM=NetworkManager
Dez 04 15:16:55 localhost systemd[1]: Starting Hostname Service...
Dez 04 15:16:55 localhost systemd[1]: Started Hostname Service.
Dez 04 15:16:55 localhost NetworkManager[693]: <info> NetworkManager (version 1.0.4) is starting...
Dez 04 15:16:55 localhost NetworkManager[693]: <info> Read config: /etc/NetworkManager/NetworkManager.conf
Dez 04 15:16:55 localhost systemd[1]: Started Network Manager.
Dez 04 15:16:55 localhost NetworkManager[693]: <info> VPN: loaded org.freedesktop.NetworkManager.pptp
Dez 04 15:16:55 localhost systemd[1]: Reached target Network.
Dez 04 15:16:55 localhost NetworkManager[693]: <info> DNS: loaded plugin dnsmasq
Dez 04 15:16:55 localhost systemd[1]: Reached target Network is Online.
Dez 04 15:16:55 localhost systemd[1]: Mounting /media/Library...
Dez 04 15:16:55 localhost systemd[1]: Starting /etc/rc.local Compatibility...
Dez 04 15:16:55 localhost NetworkManager[693]: <info> init!
Dez 04 15:16:55 localhost NetworkManager[693]: <info> update_system_hostname
Dez 04 15:16:55 localhost systemd[1]: Started /etc/rc.local Compatibility.
Dez 04 15:16:55 localhost NetworkManager[693]: <info> interface-parser: parsing file /etc/network/interfaces
Dez 04 15:16:55 localhost systemd[1]: Started Authenticate and Authorize Users to Run Privileged Tasks.
Dez 04 15:16:55 localhost NetworkManager[693]: <info> interface-parser: finished parsing file /etc/network/inter
Dez 04 15:16:55 localhost NetworkManager[693]: <info> management mode: unmanaged
Dez 04 15:16:55 localhost NetworkManager[693]: <info> devices added (path: /sys/devices/pci0000:00/0000:00:1c.1/0000:0
Dez 04 15:16:55 localhost NetworkManager[693]: <info> device added (path: /sys/devices/pci0000:00/0000:00:1c.1/0000:02
Dez 04 15:16:55 localhost NetworkManager[693]: <info> devices added (path: /sys/devices/virtual/net/lo, iface: lo)
Dez 04 15:16:55 localhost NetworkManager[693]: <info> device added (path: /sys/devices/virtual/net/lo, iface: lo): no
Dez 04 15:16:55 localhost NetworkManager[693]: <info> end _init.

The interesting sequence cut from the log above
...
Dez 04 15:16:55 localhost systemd[1]: Reached target Network is Online.
Dez 04 15:16:55 localhost systemd[1]: Mounting /media/Library...
...
Dez 04 15:16:55 localhost NetworkManager[693]: <info> init!
...
Dez 04 15:16:55 localhost NetworkManager[693]: <info> end _init.