404 Error not excluded

Hi, in my stats I tried to exclude 404 calls. I send for every not found page the 404 header. But the stats show all those calls. Under options -> exclude I activated the part exclude 404-errors.

Like that call: https://komponistinnen.org/community/?wpforo=signup

Can you help me?
Thanks, Janek

The page I need help with: [log in to see the link]