You can try changing input method, on Settings > Region and Language > Manage installed languages > Keyboard Input Method > try XIM and None. By default, you should have IBus. Or, on Region and Language you can click the gear button and select Allow different input methods for each window, thus they should use their own input method without relying on the system or user's choice. On the input method that you currently have you can click the eye button to see graphic feedbacks of the inputs you give to the keyboard, just to test.