I get a 404 when using a subdirectory for drupal/drigg.

how to reproduce:
1) I'm not logged in, drupal is running in a "drupal" subdir
2) then I submit a topic like this
http://www.domain.com/drupal/user/register?destination=drupal%252Fsubmit...
3) I click login, enter user and password
4) Login/submit button redirects to
http://www.domain.com/user?destination=drupal%252Fsubmit%253Furl
"drupal/" is missing here

thanks for your help