Formatted data is not saved correctly

Using MS Access back end. The ID field is a text field of 4 characters. 4 characters are required, and so if a product ID has less than 4 characters, the ID field gets padded to make 4 characters:

Private Sub IDTextBox_Validating(sender As System.Object, e As System.ComponentModel.CancelEventArgs) Handles IDTextBox.Validating
    While Len(IDTextBox.Text) < 4
        IDTextBox.Text = CStr("0" + CStr(IDTextBox.Text))
    End While
End Sub

When the user clicks the Save button to save the data, the leading zeros are dropped.

Private Sub SaveData()    Me.Validate()
    Me.TblProductsBindingSource.EndEdit()    Me.TableAdapterManager.UpdateAll(Me.StewardDataSet)
End Sub

Why does this happen? And how do I overcome this?