When creating a subtask it redirects to a not existing tab.

When creating a task it redirects to the `tasks` tab of the dossier. For main task this works like expected. But when creating a subtask, it redirects to the not existing `tasks` tab on the main task. Therefore it starts flickering and can't display the tab content:
![bildschirmfoto 2013-10-04 um 11 54 06](https://f.cloud.github.com/assets/485755/1268256/f369a3cc-2cda-11e3-9475-e6dbaad7ec24.png)