To reproduce: 
- Set the NullableValue property to null. 
- When you start the application there is no date in datetime picker but when the control loses the focus the date is automatically filled.

Workaround: 
- Set the NullDate to equals the Value: radDateTimePicker1.NullDate = radDateTimePicker1.Value; 
- Then you change the NullDate in the ValueChanged event: 
void radDateTimePicker1_ValueChanged(object sender, EventArgs e) { radDateTimePicker1.NullDate = new DateTime(1980, 1, 1); }