Shutdown hangs with systemd and NFS mount

I have the following line in /etc/fstab:
192.168.1.5:/srv/nsf4/main /shares nfs noauto,nofail,x-systemd.automount,_netdev,x-systemd.device-timeout=14,size=32768,wsize=32768 0 0

This works properly in the sense that systemd does not hold up the system when booting, and it does mount the directory upon first access, however the system hangs at shutdown in a manner consistent with systemd shutting down the network before attempting to unmount the drive. Indeed, even when the system is running, I can manually run

systemctl stop NetworkManager.service

and/or

systemctl stop network.target

and a call to

systemctl status shares.mount

shows that the mount is still active.

Finally, I will describe the debugging I have done to this point. First, if I manually unmount the share before shutting down, it shuts down immediately. Second, it should be noted that this does not in anyway depend on using the x-systemd.automount option. The same thing happens without automount (or fstab for that matter - simply manually mounting an NFS share and shutting down results in the computer getting stuck on the shutdown screen). I also tried adding additional items to the Require= and After= lines for shares.mount, specifically I tried adding network.target, NetworkManager.service, and wpa_supplicant.service. In each case, I did observe that manually running

systemctl stop NetworkManager.service

(for instance) now did cause the share to be unmounted, however if I shutdown the computer without manually stopping these services it would still stall on the shutdown screen. I can leave it for over 10 minutes, at which point I manually power it off.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: systemd 219-5ubuntu1
ProcVersionSignature: Ubuntu 3.19.0-10.10-generic 3.19.2
Uname: Linux 3.19.0-10-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.17-0ubuntu1
Architecture: amd64
CurrentDesktop: GNOME
Date: Tue Mar 31 09:05:25 2015
InstallationDate: Installed on 2015-03-31 (0 days ago)
InstallationMedia: Ubuntu-GNOME 15.04 "Vivid Vervet" - Beta amd64 (20150326)
MachineType: Dell Inc. Dell Precision M3800
ProcEnviron:
 TERM=xterm
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/usr/bin/fish
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-3.19.0-10-generic root=/dev/mapper/AntergosVG-UbuntuRoot ro quiet splash vt.handoff=7
SourcePackage: systemd
UdevLog: Error: [Errno 2] No such file or directory: '/var/log/udev'
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 11/14/2014
dmi.bios.vendor: Dell Inc.
dmi.bios.version: A08
dmi.board.name: Dell Precision M3800
dmi.board.vendor: Dell Inc.
dmi.board.version: A08
dmi.chassis.type: 8
dmi.chassis.vendor: Dell Inc.
dmi.chassis.version: Not Specified
dmi.modalias: dmi:bvnDellInc.:bvrA08:bd11/14/2014:svnDellInc.:pnDellPrecisionM3800:pvrA08:rvnDellInc.:rnDellPrecisionM3800:rvrA08:cvnDellInc.:ct8:cvrNotSpecified:
dmi.product.name: Dell Precision M3800
dmi.product.version: A08
dmi.sys.vendor: Dell Inc.