How do I remove duplicate icon from Ubuntu dock?

After using

jar xvf <filename>

command to unzip a file I suddenly got a second duplicate of the Files icon on my dock as you can see on the picture:

Clicking the "duplicate" icon at the bottom opens a new files window as normal but only accessible by the "real" icon as you can see from the dots aside the "real" icon. I do not have an option to remove the duplicate icon from the favorites but I do have "add to favorites" option which is quite strange. To give you more details, these duplicate icons do not appear on the dash if I search for "files".