partitioning - Ubuntu 14.04.2 installer does not recognize partitions when trying to install dual-boot alongside Windows 8.1

I'm trying to follow the guide by Luis Alvarado at Installing Ubuntu Alongside a Pre-Installed Windows with UEFI for installing Ubuntu 14.04 UEFI in dual boot with Windows 8.1.

I created the partitions from Windows, then rebooted, disabled SecureBoot (but leave UEFI enabled), booted Ubuntu from an USB stick in UEFI mode.

It runs fine (although in a 800x600 resolution), but when I reach the step where the installer asks for partitions, this is what I see (completely empty list of partitions):

I don't know how to proceed.

Maybe this can be a useful information:

root@ubuntu:~# gdisk -l /dev/sda
GPT fdisk (gdisk) version 0.8.8
Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present
Found valid GPT with protective MBR; using GPT.
Disk /dev/sda: 3907029168 sectors, 1.8 TiB
Logical sector size: 512 bytes
Disk identifier (GUID): 65315FB0-3173-43D4-BD21-7BB11E44E5D5
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 3907024613
Partitions will be aligned on 2048-sector boundaries
Total free space is 6077 sectors (3.0 MiB)
Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048         1026047   500.0 MiB   EF00  EFI system partition
   2         1026048         1107967   40.0 MiB    FFFF  Basic data partition
   3         1107968         1370111   128.0 MiB   0C01  Microsoft reserved part
   4         1370112         5564415   2.0 GiB     2700  Basic data partition
   5         5564416      1949353983   926.9 GiB   0700  Basic data partition
   6      1949353984      3064690687   531.8 GiB   0700  Basic data partition
   7      3064690688      3883890687   390.6 GiB   0700  Basic data partition
   8      3883892736      3907022598   11.0 GiB    2700  Microsoft recovery part

Partitions 6 and 7 are the ones I created by shrinking partition 5, which is the Windows 8.1 partition.

Edit:

root@ubuntu:~# hdparm -N /dev/sda
/dev/sda:
 max sectors   = 3907029168/3907029168, HPA is disabled

Edit:

gparted can correctly see all the partitions, however it gives two warning at startup:

1. The backup GPT table is not at the end of the disk, as it should be. This might mean that another operating system believes the disk is smaller.


2. Not all of the space available to /dev/sda appears to be used, you can fix the GPT to use all of the space (an extra 4521 blocks) or continue with the current setting?

May these problem be relevant with the issue in the Ubuntu installer?

Fixing the backup GPT solved the issue.

In order to fix it: run "sudo gparted", and click FIX when it reports the problem about the backup GPT and proposes to fix it).