Can't see "Track changes"

"A useful feature is the ability to track changes that have been made to an article by each contributor who has participated in the writing and editing process. Every time someone adds, removes, or moves text in an existing article, the change is highlighted in the Text Editor in InDesign or in the Text view and Article view in InCopy. You can then accept or ignore the changes.

Use the Track Changes panel in InDesign or the Track Changes toolbar in InCopy to turn Track Changes on and off and show, hide, accept, and ignore changes made by collaborators."

The problem is that I don't see any changes being made, even though all the settings seem to be set correctly. Has anyone encountered similar problems?