Order of keyboard layouts affects the behaviour of a key

I'm using two layouts in my Xubuntu 16.04 machine: "Spanish" and "English (UK)". I switch between them by using the "Keyboard Layouts" element in my xfce4 panel.

The issue seems to be that depending on the order in which I set layouts in the Keyboard/Layout window, one key (the one on the right of left-Shift, which is "\" in the UK layout and "<" in the Spanish one) will behave as if in the English layout while the Spanish layout is set.

Repro steps:
* Add a "Keyboard layout" element to your xfce4 panel for ease of switch.
* Open the Keyboard settings window (for example, by right clicking the "Keyboard layout" element in the xfce4 panel, which should look like a flag, and selecting "Keyboard settings").
* Go to "Layout" tab
* If ticked, untick "Use system defaults".
* In the "Keyboard layout" section, remove all layouts and add the following two: "English (UK)" and "Spanish" IN THIS ORDER (see attached image). (The order in which you add the entries is irrelevant, the important bit is the final order in which they are in before closing the window).
* Close the settings window.
* Switch to Spanish by clicking the British flag in the xfce4 panel (it should become the Spanish flag after clicking on it).
* Open any text editor/terminal and press the key immediately right to the left shift button. In a UK keyboard it should be "\", in a Spanish keyboard it should be "<".
* Observe how the key actually acts as the English key. If one presses Shift + the key, it shows "|" (like in an English keyboard) instead of the expected ">". All the rest of the keys seem to behave as if in a Spanish keyboard, making it impossible to type "<" or ">".

Workaround:
Placing the Spanish layout before the UK layout seems to fix this, but the order shouldn't matter.
Also, using "setxkbmap es" and "setxkbmap gb" from the terminal works fine, regardless of the order set in the Keyboard settings window.

Set up information:
$ lsb_release -rd
Description: Ubuntu 16.04.2 LTS
Release: 16.04

$ apt-cache policy xfce4-settings
xfce4-settings:
  Installed: 4.12.0-2ubuntu1
  Candidate: 4.12.0-2ubuntu1
  Version table:
 *** 4.12.0-2ubuntu1 500
        500 http://us.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
        100 /var/lib/dpkg/status

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: xfce4-settings 4.12.0-2ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-81.104-generic 4.4.67
Uname: Linux 4.4.0-81-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.6
Architecture: amd64
CurrentDesktop: XFCE
Date: Thu Jun 29 12:10:01 2017
ExecutablePath: /usr/bin/xfce4-keyboard-settings
InstallationDate: Installed on 2017-03-23 (97 days ago)
InstallationMedia: Xubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
ProcEnviron:
 LANGUAGE=en_US
 PATH=(custom, user)
 XDG_RUNTIME_DIR=<set>
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: xfce4-settings
UpgradeStatus: No upgrade log present (probably fresh install)