Front end theme is changed only for myself

Prerequisites

  • Have more than one front end theme installed

Steps to reproduce

  • Log in to Admin Area (I only have one user account, with super admin privileges)
  • Go to ‘Settings > Front end theme’
  • Change theme
  • Visit home page
  • In a private browser window visit home page

What should happen

  • Both regular session and private session should display home page from the same theme, the one that was selected.

What happens instead

  • Regular session displays home page from the newly selected theme, while the private session displays home page from the old theme.

Questions

  • What is the canonical method of activating a front end theme in October CMS? Where can I find any User Guides?
  • Why is my selected theme only activated for one user?
  • Where is the active theme setting stored? Is it in database? If yes, which table?