Another bound date time picker question

I am using a date time picker which is bound to a datatable with a custom format.

                //datetime picker 
                this.dtpInvoiceDate.DataBindings.Clear();
                this.dtpInvoiceDate.DataBindings.Add(new Binding("Value", bsHeader, "APINHINVOICEDATE", true));

It is set to the current date on the form load.

If the dtp is not selected the date never gets written to the table.

Is there some magic formula needed for this to happen????

VS .net4 2012 c#