DateTimePicker problem

I have a problem with a DTPicker in my WindowsForm.
The DTPicker is CheckBoxed (ShowCheckBox = true) and is bound to a data source (a data(as string) colum in a table).

In the format event of the DTPicker's Binding object, I have to check the column value and if it's a null string I want to set the DTPicker to the current date and uncheck it. But it does not want to uncheck itself. It remains checked.

Implicitly the DTPicker is unchecked but when i set it's value to the current date it check itself automaticaly.

Here is my portion of code :

private void StringToDate(object sender, ConvertEventArgs cevent) {
string date = (string)cevent.Value;
if (date==" - -") {
cevent.Value=DateTime.Now;
dtp_datalimita.Checked=false;
return;
}
......
}

The "checked" property of "dtp_datalimita" is set on false but the DTPicker is shown as checked.
I tryed "dtp_datalimita.Refresh" after "dtp_datalimita.Checked=false;" but it does not work.

Did enyoane encounter a similar problem ?
Is this a bug?
Is there a solution to my problem?

Thanks to all that will find enough time to look on to this piece of paper !

My address

What language and platform is this for?

Sorry, I forgot to mention this: The language is C# on Microsoft Visual Studio .NET

I did find a strange sollution to this and it is very easy.

dtp.Checked = false;

does not work.

dtp.Checked = true;
dtp.Checked = false;

Seems to work fine!