setting personal preferences in admin UI fails

Steps to reproduce:
1. Click on the drowndown with your user name in the upper right and select "preferences"
2. Fill out the form and press "save"
3. While loading the form and saving it you get an error 404 for the URL http://roe.virtuos.uos.de:8080/admin-ng/user-settings/signature
4. Re-opening "preferences" opens an empty form.