Super+Space not working on Unity 17.10

Question

Until 17.10 I mostly used Unity and never had this issue (I had GNOME installed and seldom used it). But since the upgrade I switched to GNOME, where the shortcut works and I find it better because it cycles through sources in the recently used order.

After a few months I decided to reinstall Ubuntu because it was too laggy, so the Unity session I have now was installed manually later. Then I noticed that it was GNOME especially that was too laggy on my 4GB RAM laptop, so I moved back to Unity which is much more fluid.

Here comes the issue, pressing Super+Space doesn't switch the input sources, and the weirdest thing is that Shift+Super+Space shows and horizontal switcher for English and French, instead of the vertical drop-down switcher from the panel where I don't even have an English source (I have French, Japanese and Belgian sources).

Note : I noticed that other shortcuts that use the Super key don't work as well as the other shortcuts : i.e. Super+E which I set to open nautilus as root only works when I press Super then E then release E and finally release Super. I don't remember having a 'release order' before, could it be related to the issue ?

Note 2 : I know I can bind another shortcut for this task (and it works), but I find the default one pretty good and I don't like this Super key malfunction.

UPDATE

About the input sources showed when I do Shift+Super+Space (English and French), I found that they are the same as in Fcitx Configuration (which key binding is set to Ctrl+Space) and as in IBus Preferences (which key binding was also set to Super+Space, but I set it to something else to test, however Super+Space still does not work).

Answer 1

Ubuntu 17.10 solution:

1. Run ibus-setup
2. Disable shortcut for changing layouts (delete it).
3. Set Super+Space shortcut in System Settings -> Keyboard.

It's a conflict between IBus and System Settings shortcuts.

Answer 2

The shortcut was bound to something else and the other actions bound to Super+Space were not executed.

I was wondering why sushi wasn't working on nautilus when I noticed that what I wanted was gnome-sushi, so I uninstalled (and purged) sushi and now Super+Space allow me to switch between the IBus input sources.

As the IBus input sources are not the same as the ones I setted through the System Settings, I changed IBus key binding (can be done by typing ibus-setup in terminal).

I still don't know why the IBus (and the fcitx) input sources aren't the same as the ones in System Settings, but my problem is solved.

EDIT : I had this issue again, so it might not have been sushi (but maybe it was sushi first, and something else after that), but I have found a work-around which is to switch back to lightdm (which is fine to me since it is more continuous than gdm with Unity).