I'm having trouble with a simple table edit in a Winform application. I must have missed a step.

I have a DataSet containing a DataTable connected to a database with a SqlDataAdapter. There is a SqlCommandBuilder on the SqlDataAdapter. On the form, there are TextBoxes which are bound to the DataTable. The binding was done in the Designer and it machine-produced statements like this:

this.tbLast.DataBindings.Add(new System.Windows.Forms.Binding("Text", this.belkData, "belk_mem.last", true));

When I fill the row in the DataTable, the values from the database appear in the textboxes, but when I change contents of the TextBox, the changes are apparently not being going to the DataTable. When I try to save change both of the following return null:

  DataTable dtChanges = dtMem.GetChanges();
  DataSet dsChanges = belkData.GetChanges();

What did I forget?

Edit - response to mrlucmorin:

The save is under a button. Code is:

    BindingContext[belkData, "belk_mem"].EndCurrentEdit();

    try
    {
        DataSet dsChanges = belkData.GetChanges();
        if (dsChanges != null)
        {
            int nRows = sdaMem.Update(dsChanges);
            MessageBox.Show("Row(s) Updated: " + nRows.ToString());
            belkData.AcceptChanges();
        }
        else { MessageBox.Show("Nothing to save.", "No changes"); }
    }
    catch (Exception ex)
    {
        MessageBox.Show("Error: " + ex.Message);
    }

I've tried putting in these statements without any change in behavior:

   dtMem.AcceptChanges();
   belkData.AcceptChanges();