title: Custom error page configured in IIS for code 400 (bad request) is ignored
body: <p>For my website I configured some custom error pages.
  If I generate a 404, the redirect works fine.
  When hitting a 400, the "bad request" text shows up instead of the configured URl.</p>
  
  <p>As a test I copied the URL from 404 to 400. No change.
  Then I changed the redirect to a file. No change.</p>
  
  <p>Any ideas?</p>