Fluent NHibernate Problems with SQL Server 2008 DATE Column Values

Greetings,

I'm having problems using a SQL Server 2008 DATE column in C# using Fluent NHibernate.

When I try to update a record that has a value in a non-nullable DATE column prior to 1/1/1753 (the min date for a DATETIME), I'm getting an error saying that it can't insert a NULL into that column. If the value is greater than 1/1/1753, there are no problems and the correct date value is preserved.

Here's my model file:

public class Table1 : model.DBObject
{
  public virtual Int32 TestID { get; private set; }
  public virtual String Description { get; set; }
  public virtual DateTime TestDate { get; set; }

  public Table1()
  {
  }

  public static Table1 Load(DBSess sess, Int32 TestID)
  {
      return (Table1)sess.Session.Get(typeof(Table1), TestID);
  }
}

My mapping file:

public class Table1Map : ClassMap<Table1>
{
  public Table1Map()
  {
    Table("[Table1]");
    Id(x => x.TestID).GeneratedBy.Identity();
    Map(x => x.Description).Not.Nullable();
    Map(x => x.TestDate).Not.Nullable().CustomType("date");
  }
}

The code being executed:

using (DBSess sess = DBSess.Create())
{
  Table1 tbl = dal.Table1.Load(sess, 1);
  tbl.Description = String.Format("Updated {0}", DateTime.Now);
  tbl.Save(sess);
  sess.Commit();
}

The exported NHibernate mappings:

<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2" default-access="property" auto-import="true" default-cascade="none" default-lazy="true">
  <class xmlns="urn:nhibernate-mapping-2.2" mutable="true" name="dal.Table1, dal, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" table="[Table1]">
    <id name="TestID" type="System.Int32, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089">
      <column name="TestID" />
      <generator class="identity" />
    </id>
    <