Webform not send when alias is "update"

I recogniced a strange behaviour and I needed some time to get close to the problem. On my site there are many webforms and all of them make no problems but one. The one I mean, as filled out and sent, don't save the data and don't show the success message. It only brings you back to the webform. I spent hours to get an idea about what the problem is. Now I'm nearly sure that the alias is the problem. It was "update" because the event for what you can subscribe on the webform is called so. When I call the webform with its node name, everything is well and also when I change the alias to anything else.

Can it be, that Drupal has a problem with the alias because it is needed for the update procedure (update.php)? But then there must be a warning when ones try to set this alias. The situation now behaves like a bug to me.