SQL Server Full-Text Index crawl: Is it done or not?
Since you have Change Tracking = AUTO configured you are telling the SQL Server to check on the changes that being made in the FULL TEXT INDEX. That means that the process is still running at a low level.

I would not be at all surprised to see some activity as the Full Text Indexing service is checking for changes. 

Populate Full-Text Indexes for SQL Server 2012  

A similar question was asked here back in 2013: 

Full Text Search Populate Status - Processing notifications 

Quoting from Frank J Garcia's answer:   


  There is a small overhead associated with change tracking because SQL Server maintains a table in which it tracks changes to the base table since the last population. When change tracking is used, SQL Server maintains a record of the rows in the base table or indexed view that have been modified by updates, deletes, or inserts.