Thank you for reply, David!

>I have an idea of what's wrong here but before I speculate on that, what exactly does "enable automount" mean? Are you referring to having the 'auto' option in the /etc/fstab file?

By "enable automount" I mean these dconf-editor parameters: org.gnome.desktop.media-handling.automount and org.gnome.desktop.media-handling.automount-open (see comment #5). So if I set both parameters to true (in dconf-editor) I get all two partitions of my drive mounted in Nautilus on device connection.

>When the system is running with the WD USB-HDD, please include the output of 'gvfs-mount -li' from a non-root shell in a terminal in the desktop session.

The output of 'gvfs-mount -li' for my WD USB-HDD is as follows:
	Drive(3): WD My Passport 0743
	  Type: GProxyDrive (GProxyVolumeMonitorUDisks2)
	  ids:
	   unix-device: '/dev/sdc'
	  themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	  symbolic themed icons:  [drive-harddisk-usb-symbolic]  [drive-harddisk-symbolic]  [drive-symbolic]  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	  is_media_removable=0
	  has_media=1
	  is_media_check_automatic=1
	  can_poll_for_media=0
	  can_eject=0
	  can_start=0
	  can_stop=1
	  start_stop_type=shutdown
	  sort_key=01hotplug/1391451089446989
	  Volume(0): WD_2TB_NTFS
	    Type: GProxyVolume (GProxyVolumeMonitorUDisks2)
	    ids:
	     class: 'device'
	     unix-device: '/dev/sdc2'
	     uuid: '32BA1ADB5E526052'
	     label: 'WD_2TB_NTFS'
	    themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	    symbolic themed icons:  [drive-harddisk-usb-symbolic]  [drive-harddisk-symbolic]  [drive-symbolic]  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	    can_mount=1
	    can_eject=0
	    should_automount=1
	    sort_key=gvfs.time_detected_usec.1391451089661368
	  Volume(1): WD_2TB_EXT4
	    Type: GProxyVolume (GProxyVolumeMonitorUDisks2)
	    ids:
	     class: 'device'
	     unix-device: '/dev/sdc1'
	     uuid: '6d296a81-e054-4e09-a092-cee6a0041e0c'
	     label: 'WD_2TB_EXT4'
	    themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	    symbolic themed icons:  [drive-harddisk-usb-symbolic]  [drive-harddisk-symbolic]  [drive-symbolic]  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	    can_mount=1
	    can_eject=0
	    should_automount=1
	    sort_key=gvfs.time_detected_usec.1391451089662205
	    Mount(0): WD_2TB_EXT4 -> file:///run/media/flash/WD_2TB_EXT4
	      Type: GProxyMount (GProxyVolumeMonitorUDisks2)
	      default_location=file:///run/media/flash/WD_2TB_EXT4
	      themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	      symbolic themed icons:  [drive-harddisk-usb-symbolic]  [drive-harddisk-symbolic]  [drive-symbolic]  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	      can_unmount=1
	      can_eject=0
	      is_shadowed=0
	      sort_key=gvfs.time_detected_usec.1391451089941622


For my Seagate HDD I have:


	Drive(3): ST950042 0AS
	  Type: GProxyDrive (GProxyVolumeMonitorUDisks2)
	  ids:
	   unix-device: '/dev/sdc'
	  themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	  symbolic themed icons:  [drive-harddisk-usb-symbolic]  [drive-harddisk-symbolic]  [drive-symbolic]  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	  is_media_removable=0
	  has_media=1
	  is_media_check_automatic=1
	  can_poll_for_media=0
	  can_eject=0
	  can_start=0
	  can_stop=1
	  start_stop_type=shutdown
	  sort_key=01hotplug/1391451261668976
	  Volume(0): NTFS
	    Type: GProxyVolume (GProxyVolumeMonitorUDisks2)
	    ids:
	     class: 'device'
	     unix-device: '/dev/sdc2'
	     uuid: '5F6174ED0C58C4B3'
	     label: 'NTFS'
	    themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	    symbolic themed icons:  [drive-harddisk-usb-symbolic]  [drive-harddisk-symbolic]  [drive-symbolic]  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	    can_mount=1
	    can_eject=0
	    should_automount=1
	    sort_key=gvfs.time_detected_usec.1391451261990760
	    Mount(0): NTFS -> file:///run/media/flash/NTFS
	      Type: GProxyMount (GProxyVolumeMonitorUDisks2)
	      default_location=file:///run/media/flash/NTFS
	      themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	      symbolic themed icons:  [drive-harddisk-usb-symbolic]  [drive-harddisk-symbolic]  [drive-symbolic]  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	      can_unmount=1
	      can_eject=0
	      is_shadowed=0
	      sort_key=gvfs.time_detected_usec.1391451263178059
	  Volume(1): GENTOO
	    Type: GProxyVolume (GProxyVolumeMonitorUDisks2)
	    ids:
	     class: 'device'
	     unix-device: '/dev/sdc1'
	     uuid: '52e2b7ea-21e0-4973-aeae-f5b7edfadf40'
	     label: 'GENTOO'
	    themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	    symbolic themed icons:  [drive-harddisk-usb-symbolic]  [drive-harddisk-symbolic]  [drive-symbolic]  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	    can_mount=1
	    can_eject=0
	    should_automount=1
	    sort_key=gvfs.time_detected_usec.1391451261992313
	    Mount(0): GENTOO -> file:///run/media/flash/GENTOO
	      Type: GProxyMount (GProxyVolumeMonitorUDisks2)
	      default_location=file:///run/media/flash/GENTOO
	      themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	      symbolic themed icons:  [drive-harddisk-usb-symbolic]  [drive-harddisk-symbolic]  [drive-symbolic]  [drive-harddisk-usb]  [drive-harddisk]  [drive]
	      can_unmount=1
	      can_eject=0
	      is_shadowed=0
	      sort_key=gvfs.time_detected_usec.1391451262121538
	

I hope this help you to understand the problem.