Hi Timo,
This can be achieved easily with the help of a Non-persistable entity on a page.
Create a nonpersistable entity that looks similar to your persistable entity and use the same in your form.
When you click on save, create a new persistable object and commit to the database. Empty the fields in the nonpersistable object while saving the form so that you can use the same nonpersistable object to create a new object again.
You made my day :-)
In addition I changed the actualize interval in the DataGrid2 to 1 second and it works exactly as needed.