language is filtered in lock-screen's language selector

After installing Ubuntu 16.04 I've changed text entry settings to contain two languages as follows:
1) Korean (Hangul)(IBus)
2) Russian
Korean IM can produce both - English (default) & Hangul characters, so having one more English (US) is not needed and confusing.

When the screen is locked by pressing Super+L or automatically after timeout, language selector contains just one item - Russian, which is totally useless to enter normal passwords. So the screen is effectively locked out without the possibility to unlock the session.

I would expect to see Korean IM with Hangul character composing disabled, or at least English (US) temporarily added to the list instead of Korean, if it must be filtered out.

System Info:
# lsb_release -rd
Description: Ubuntu 16.04 LTS
Release: 16.04
# apt-cache policy gnome-screensaver
gnome-screensaver:
  Installed: 3.6.1-7ubuntu4
  Candidate: 3.6.1-7ubuntu4
  Version table:
 *** 3.6.1-7ubuntu4 500
        500 http://kr.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: gnome-screensaver 3.6.1-7ubuntu4
ProcVersionSignature: Ubuntu 4.4.0-22.40-generic 4.4.8
Uname: Linux 4.4.0-22-generic x86_64
NonfreeKernelModules: symap_custom_4_4_0_22_generic_x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
CurrentDesktop: Unity
Date: Wed Jun 8 15:12:00 2016
GnomeSessionIdleInhibited: No
GnomeSessionInhibitors: None
GsettingsGnomeSession:
 org.gnome.desktop.session session-name 'ubuntu'
 org.gnome.desktop.session idle-delay uint32 300
InstallationDate: Installed on 2016-06-01 (7 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
SourcePackage: gnome-screensaver
UpgradeStatus: No upgrade log present (probably fresh install)