Comment 7 for bug 1890875

I have tried to add an input source through gsettings
gsettings set org.gnome.desktop.input-sources sources "[('xkb', 'us'), ('xkb', 'ru')]"
but it still produced the same result: text input remains at default layout.

Restarting the GNOME Shell fixes the issue and the 'ru' layout gets added in /etc/default/keyboard configuration file: XKBLAYOUT=us,ru

This may explain why rearranging the order of input sources magically fixes the bug: newly added input sources probably need to be put into defaults once to be recognized later.

However, manually editing the keyboard configuration file does nothing.

What probably happens is that gnome-shell recognizes the added input sources but 'forgets' 1) to send the appropriate command to XKB (setxkbmap ru) whenever the switch shortcut is invoked; or 2) to reconfigure the keyboard settings.