Using the im-chooser tool, XIM cannot be disabled as the default GTK immodule. Disabling input-methods using im-chooser and restarting the desktop session will still result in GTK applications using the XIM immodule. Consequently, using the Ctrl+Shift+U key combination to the directly input of Unicode characters from their hexidecimal code will not work. To work around this issue, use im-chooser to enable ibus. Enabling ibus permits gtk-im-context-simple's Unicode input and compose sequences to be used.