This article explains why you should never click the Back button on your browser when editing articles

When you are editing an article in Joomla you should not click the Back button on your browser.  This is because the article is 'locked' for editing whilst you are in it.  Instead all you need to do is click the Save, Apply or Cancel buttons.

Save = Saves the changes you have made to the article and closes it (taking you to the Article Manager view)

Apply = Saves the changes you have made to the article and keeps it open

Cancel = Does not save any changes you have made and closes it

Unlocking Articles

You can tell when administrators are using the browser back button in the Article Manager view as you will see the locked  icon against several articles.

Articles that are locked cannot be edited.

To unlock them all come out of any articles then click on Tools (top right ) then Global Check in.