Channel manager: subsite - Unable to have different items in left/right containers across pages for subsite

1. Login to CMS
2. Navigate to channel manager
3. Select any sub-site channel >> click on open channel >> go to edit mode (where you see template composer)
4. Now add or delete an item from left or right side of the page

Expected - The item should be added or deleted only in that page
Actual - The item is added or deleted across all the pages (home, about, programme,... etc)