Oh, I agree it's not directly relevant to the bug. But it does demonstrate the lengths to which I had to resort to work around this (and other) Nautilus problems.

I plug an external, two-partition USB disk in, both partitions appear in Nautilus (neither is available as a drop target), but I don't click on either. gvfs-mount -li reports this:

Drive(0): 320 GB Hard Disk
  Type: GProxyDrive (GProxyVolumeMonitorGdu)
  ids:
   unix-device: '/dev/sdb'
  themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
  is_media_removable=0
  has_media=1
  is_media_check_automatic=0
  can_poll_for_media=0
  can_eject=0
  can_start=0
  can_stop=1
  start_stop_type=shutdown
  Volume(0): Windows XP System Disk
    Type: GProxyVolume (GProxyVolumeMonitorGdu)
    ids:
     uuid: 'DC6073B7607396CC'
     unix-device: '/dev/sdb1'
     label: 'Windows XP System Disk'
    themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
    can_mount=1
    can_eject=0
    should_automount=1
    Mount(0): Windows XP System Disk -> file:///media/Windows%20XP%20System%20Disk
      Type: GProxyMount (GProxyVolumeMonitorGdu)
      default_location=file:///media/Windows%20XP%20System%20Disk
      themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
      can_unmount=1
      can_eject=0
      is_shadowed=0
  Volume(1): Portable Media
    Type: GProxyVolume (GProxyVolumeMonitorGdu)
    ids:
     uuid: '2768D14E2E43D1D2'
     unix-device: '/dev/sdb2'
     label: 'Portable Media'
    themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
    can_mount=1
    can_eject=0
    should_automount=1
    Mount(0): Portable Media -> file:///media/Portable%20Media
      Type: GProxyMount (GProxyVolumeMonitorGdu)
      default_location=file:///media/Portable%20Media
      themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
      can_unmount=1
      can_eject=0
      is_shadowed=0
Drive(1): CD/DVD Drive
  Type: GProxyDrive (GProxyVolumeMonitorGdu)
  ids:
   unix-device: '/dev/sr0'
  themed icons:  [drive-optical]  [drive]
  is_media_removable=1
  has_media=0
  is_media_check_automatic=1
  can_poll_for_media=1
  can_eject=0
  can_start=0
  can_stop=0
  start_stop_type=unknown
Volume(2): cdrom2
  Type: GProxyVolume (GProxyVolumeMonitorGdu)
  themed icons:  [drive-optical]  [drive]
  can_mount=1
  can_eject=0
  should_automount=0

I click the disk and it's now available as a drop target. gvfs-mount -li reports this:

Drive(0): 320 GB Hard Disk
  Type: GProxyDrive (GProxyVolumeMonitorGdu)
  ids:
   unix-device: '/dev/sdb'
  themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
  is_media_removable=0
  has_media=1
  is_media_check_automatic=0
  can_poll_for_media=0
  can_eject=0
  can_start=0
  can_stop=1
  start_stop_type=shutdown
  Volume(0): Windows XP System Disk
    Type: GProxyVolume (GProxyVolumeMonitorGdu)
    ids:
     uuid: 'DC6073B7607396CC'
     unix-device: '/dev/sdb1'
     label: 'Windows XP System Disk'
    themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
    can_mount=1
    can_eject=0
    should_automount=1
    Mount(0): Windows XP System Disk -> file:///media/Windows%20XP%20System%20Disk
      Type: GProxyMount (GProxyVolumeMonitorGdu)
      default_location=file:///media/Windows%20XP%20System%20Disk
      themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
      can_unmount=1
      can_eject=0
      is_shadowed=0
  Volume(1): Portable Media
    Type: GProxyVolume (GProxyVolumeMonitorGdu)
    ids:
     uuid: '2768D14E2E43D1D2'
     unix-device: '/dev/sdb2'
     label: 'Portable Media'
    themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
    can_mount=1
    can_eject=0
    should_automount=1
    Mount(0): Portable Media -> file:///media/Portable%20Media
      Type: GProxyMount (GProxyVolumeMonitorGdu)
      default_location=file:///media/Portable%20Media
      themed icons:  [drive-harddisk-usb]  [drive-harddisk]  [drive]
      can_unmount=1
      can_eject=0
      is_shadowed=0
Drive(1): CD/DVD Drive
  Type: GProxyDrive (GProxyVolumeMonitorGdu)
  ids:
   unix-device: '/dev/sr0'
  themed icons:  [drive-optical]  [drive]
  is_media_removable=1
  has_media=0
  is_media_check_automatic=1
  can_poll_for_media=1
  can_eject=0
  can_start=0
  can_stop=0
  start_stop_type=unknown
Volume(2): cdrom2
  Type: GProxyVolume (GProxyVolumeMonitorGdu)
  themed icons:  [drive-optical]  [drive]
  can_mount=1
  can_eject=0
  should_automount=0

I'm no expert but those look the same to me.

I think it's being mounted ok because icons for the two partitions appear in the notification area and on the desktop, and I can cd into the partitions from the command line. I can also drag and drop directly onto the disk icons on the desktop without trouble. It's just drag and drop inside the Nautilus file manager that doesn't work.