No changes are saved to SQLCE Database

Hi,
i have a problem with my SqlCe database. Everytime i add or edit date, als seems to be fine. But the changes are not made in the database. It seems like nhibernate is caching them.
Here is a example:
I configure my database like this:

                sessionFactory = Fluently.Configure()
                                        .Database(MsSqlCeConfiguration.Standard.ShowSql().ConnectionString(@"Data Source=db\KD.sdf"))
                                        .Mappings(m => m.FluentMappings.AddFromAssemblyOf<Manufacturer>())
                                        .BuildSessionFactory();

Now, i have a simple table with an ID and some varchars.

[DebuggerDisplay("{Name}")]
public class Manufacturer
{
    public virtual int Id { get; private set; }
    public virtual String Name { get; set; }
    public virtual String ShortName { get; set; }
    public virtual String Link { get; set; }
}

and my mapping:

public class ManufacturerMap : ClassMap<Manufacturer>
{
    public ManufacturerMap()
    {
        Id(x => x.Id);
        Map(x => x.Name);
        Map(x => x.ShortName);
        Map(x => x.Link);
    }
}

now, i add a manufactuer:

        using (var session = SessionHelper.OpenSession())
        {
            using (var trans = session.BeginTransaction())
            {
                var test_manu = new Manufacturer { Name = "TestManu", ShortName = "TM", Link = "http://www.test.com/" };
                session.Save(test_manu); 

                trans.Commit();
            }
            session.Flush();
        }

that all works fine!
now, when i try to read him, everything is fine:
var test = session.CreateCriteria(typeof(Manufacturer)).List();

now, i close the application, and take a look in the database. nothing in there!

Does anyone have an idea why its empty?