Keyboard layout indicator does not update if user sets "while pressed" shortcut

Steps to reproduce:
1. Install Ubunu 18.04 LTS
2. Add two keyboard layouts (for example, English and Russian)
3. Install GNOME Tweaks (`sudo apt install gnome-tweaks`)
4. Launch GNOME Tweaks
4.1. click on *Keyboard & Mouse* group
4.2 In *Keyboard* section click *Additional Layout Options* button
4.3. In opened window expand *Switching to another layout*
4.4. Check checkbox named *Right Alt (while pressed)* (for example).
4.5. Close GNOME Tweaks windows
5. Test layout switching - press <RightAlt> and write some text

Expected results:
* keyboard layout indicator shows second keyboard layout when user holds <RightAlt> button and shows the first when it is not pressed

Actual results:
* keyboard layout indicator shows only the first keyboard layout

ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: gnome-settings-daemon 3.28.1-0ubuntu1
ProcVersionSignature: Ubuntu 4.15.0-22.24-generic 4.15.17
Uname: Linux 4.15.0-22-generic x86_64
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CurrentDesktop: ubuntu:GNOME
Date: Fri Jun 29 16:42:28 2018
InstallationDate: Installed on 2018-04-28 (61 days ago)
InstallationMedia: Ubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
SourcePackage: gnome-settings-daemon
UpgradeStatus: No upgrade log present (probably fresh install)