How to change the "Alternative switch to next source"

I have been using Ubuntu 17.10 for a while and is working great. But today after the update, I have a new shortcut, Alt+Shift, as an alternative Switch to the next input source. Alt+Shift is a common modifier in Intellij so a lot of shortcuts doesn't work any more.

I tried to change the shortcut but it is not listed in the shortcuts window.

Is there a file where I can change it (the alternative)?

Here is the screenshot of the option

Finally I found the option. I had to install Tweaks and go to

Keyboard and mouse > Additional layout options > switching to another layout

The strange thing is that there is that the default shortcut super+space was not selected in that window, only the alternative shortcut.

In my answer I assume that you use Gnome 3.x.

You can use Tweaks, but you can also write the value directly, for example, changing from Alt+Shift to Ctrl+Shift can be done by the following command in terminal:

dconf write /org/gnome/desktop/input-sources/xkb-options ['grp:ctrl_shift_toggle','grp_led:scroll']

To disable the option of alternative switch to the next source type in terminal:

xkbopts="/org/gnome/desktop/input-sources/xkb-options"
dconf read $xkbopts
dconf write $xkbopts "['']"

This worked for me. No reboot is necessary.

For Ubuntu 18.04: Alternative switch to next source Can Changed or Disabled only with "Tweak Tool":

$ sudo add-apt-repository universe
$ sudo apt install gnome-tweak-tool
$ gnome-tweaks

and then Keyboard & Mouse > Additional Layout Options > Switching to another layout