Using Ubuntu 16.04 Desktop with Unity, used the same approach in 14.04 with no issue.
I prepare for mounting with the following entry in /etc/fstab my Synology NAS :
//192.168.178.61/data /media/server/server_data cifs users,uid=1000,gid=1000,username=xxxxx,passwd=xxxxxx,iocharset=utf8,sec=ntlm,noauto,_netdev 0
After login to unity, I mount it with a bash-script (mount -a) which is called from ~/.config/autostart/myMounts.desktop
Doing this, and shuting down or rebooting lead into a very delayed shutdown (round about 2 minutes) Pressing ESC Key, showed that the process stops at the command "umount /media/server ..."
I have not tested if this also occurs when I am connected via ethernet. I think it is because the (Wifi)Network is already disabled prior all umounts are done.
This issue happens even if I type in a shutdown command into a Terminal or if I choose shutdown form the menue, also if I use the power-button.
Failure can be avoided if I umount the network-drives manually previouse to reboot.
Interim solution was, to create an alias for "shutdown" like "sh /path/to/umount/script.sh && shutdown" in /etc/bash.bashrc.local.
Just installed an automated update to Kernel 4.4.0-22-generic. Now, the workarround with the "aliases" has also stopped working.
Unable to shutdown Ubuntu with mounted CIFS (only after 120 sec. of trying and finnaly failing...)