Still having 404 issues with Drupal

Hi,

I am using Drupal 5.2, Cleanurls, Pathauto and Global Redirect enabled.
Drupal is throwing correct 404 in most cases, BUT
Drupal doesnt throw 404 for all urls with the following pattern:
http://example.com/myContentType/doesnotexist

You can see this Issue live:
http://drupal.org/forum/doesnotexist

Maybe this could be exploited by someone and hurt your SE rankings.
Has anyone a workaround for this? Or don't you see this as an issue?