I managed to install Ubuntu in a sony vaio laptop with Windows 8 pre-installed and updated to Windows 8.1. After I finished the process, I experienced the same behavior than "landroni" (How to fix dual-booting Windows 8 and Ubuntu 14.04 on a Sony Vaio?). However, I do not need to enable External device boot, as he says at the final of his post.
The boot-repair tool generated this url (http://paste.ubuntu.com/8048145/). I understand that boot-repair tries to modify the boot order in the machine by pointing to GRUB.
In this site (http://www.zdnet.com/my-experiments-with-multi-boot-selection-with-uefi-boot-manager-7000013627/), the author explains how to manually change the bootloader, however, by looking into the report generated by boot-repair, I saw there are three bootmgfw.efi files in three different partitions (sda1, sda2 and sda3). I am afraid to mess things up by chosing the wrong file. Can anyone help?