Changing the input method as PutzKipa explains actually fixes the problem.

However, I've failed to find any configuration panel under KDE ubuntu 14.04 to do the job, and the standard im-config utility seems broken. I finally succeeded by creating a file ~/.xinputrc that contains a single line:

run_im xim

then logout/login. This chooses xim as the input method (ibus is the default). If you remove your ~/.xinputrc, then im-config can list the input methods available, even if it fails to select one.

For Ubuntu 18.04.

I struggled with this problem for two days. I tried all the methods listed here earlier. And it looks like I came up with a solution. But it is very unstable and has bugs.

The basic idea is this: in the system settings you can specify the command that is started by the Ctrl+Shift+U key combination.

Note: if you specify false as the command, the combination will not work at all.

However, we can specify the path to the script as the command, in which we will simulate pressing the same key combination.

To simulate keystrokes, I tried the xdotool (apt install xdotool) and the xte (apt install xautomation).
Both options were unstable. However, xte turned out to be more flexible for me.

Example with xte

• Create a file /home/username/shortcut.sh
  


• Add permission to execute: chmod u+x /home/username/shortcut.sh
  


• Specify the path to the script as a command for the Ctrl+Shift+U key combination in the keyboard settings

Here is an example script:

#!/bin/sh

# Make a small delay in order to have time to release the keys.

sleep 0.2



# Simulate the release of just pressed keys, if they are still pressed.

xte 'keyup u' 'keyup Shift_L' 'keyup Control_L'



# Hack: Caps_Lock is used so that the system does not intercept this combination.

# You can try to remove it if it hinders you.

xte 'key Caps_Lock'



# Simulate pressing a key combination

xte 'keydown Shift_L' 'keydown Control_L' 'key u'



# Simulate releasing a key combination

xte 'keyup Shift_L' 'keyup Control_L'



# Restore Caps_Lock to the previous state.

xte 'key Caps_Lock'

I tested this in PhpStorm 2018.2 EAP Build #PS-182.3458.35 and I can say that it works, but with some caveats:

• this works slowly (on my rather old PC)


• during the execution of the script, it is better not to press any keys


• sometimes it may not work


• sometimes it can enter an infinite loop. Therefore, it's better to add a check to the script that the script is already running.

In general, if you do not often use this combination, then this solution may suit you.

But, probably, someone will come up with a better and more stable solution.

I hope this idea will help someone.

Try:

export GTK_IM_MODULE="gtk-im-context-simple"

and then run Eclipse from the same shell. Or if that doesn't work,

export GTK_IM_MODULE="xim"

(This test only works entering running the export command and then Eclipse from the same shell command line, it won't change anything if you use a desktop shortcut or the Applications menu, or run Eclipse from a new shell.)

If either test works, you can make the change system-wide by adding it to /etc/environment, or per-user in ~/.gnomerc. (The export command doesn't go in those files, just a new line with GTK_IM_MODULE="xim" or GTK_IM_MODULE="gtk-im-context-simple".)

It sounds like this behavior comes from GTK's input mappings as described here: https://developer.gnome.org/gtk3/unstable/GtkIMContext.html

... This is called preediting, and an input method may provide feedback about this process by displaying the intermediate composition states as preedit text. For instance, the default GTK+ input method implements the input of arbitrary Unicode code points by holding down the Control and Shift keys and then typing “U” followed by the hexadecimal digits of the code point. When releasing the Control and Shift keys, preediting ends and the character is inserted as text. Ctrl+Shift+u20AC for example results in the € sign.

GTK is used by a whole lot of common apps in Ubuntu, including Eclipse.

Ubuntu 14.04/18.04 Solution

recently upgrade to 18.04 and fight my way to solve this issue.

1. open search using super key


2. go to language support
   


3. click Keyboard input method system dropdown menu and choose none
   

4. 
   dont forget to click - apply system wide
   


5. close the window (wont activate until you do)


6. reboot (logout might be enough)

Credit goes to reverse issue on askubuntu - for some reason someone wants to enable this shortcut.

Ubuntu 18.04

Running into this problem on Ubuntu 18.04, I've tried all suggestion above, but unfortunately none of them worked. I ended up uninstalling the ibus package.

Background / sidenotes

I tried to disable IBus using

1. the Language Support menu


2. 
   im-config (configures ~/.xinputrc)


3. 
   sudo im-config (configures /etc/X11/xinit/xinputrc)

I noticed however that no matter what config I tried, the ibus daemon was running everytime after I had rebooted.

1. Run ibus-setup from the terminal (or open IBus Preferences).


2. Go to “Emoji”.


3. Next to “Unicode code point:”, click on the three dots (i.e. ...).


4. In the dialog, click “Delete”, then “OK”.


5. Close the IBus Preferences window.

Open a terminal window.

cd ~/.gconf/desktop/gnome/interface

gedit %gconf.xml

Change the show_unicode_menu from true to false.

Save, Log out and back in.