Right Alt key is suddenly switched off after invoking Settings - Keyboard Shortcuts in 3.35
As soon as the Keyboard Shortcuts tab window is invoked in the Settings application, Right Alt key is switched off system-wide. This happens suddenly even without any action from the user - just simple invoking of the window is enough to break the settings.
This obviously happens because of the new setting in the Keyboard Shortcuts appeared in 3.35: Alternate Characters Key. It sets Right Alt by default immediately as this window is opened. This setting doesn't have a Not-Set option, so it is not easy to switch back to the normal behavior. This setting can be unset only through the GNOME Tweaks application: Keyboard & Mouse - Additional Layout Options - Key to choose the 3rd level - uncheck the box Right Alt. But this is not a good workaround since the Right Alt key setting will be destroyed again as soon as Keyboard Shortcuts are visited in Settings next time.
A reasonable workaround seems to be introduction an option Not Set in the setting Alternate Characters Key and making it default. This will fix the bug and will introduce a sane default value because not every keyboard layout has a third-option for the keys.
This seems to be quite significant UX flaw since nothing should be changed without explicit user action.