Use the attached project and the following steps:
When the application starts, the entire content of the picker control is selected (which is fine).
Now press the Del key to clear the entire content.
If you then try and type in a date any key you type is shown briefly and is then cleared.
It is impossible to type anything until you open the drop down calendar and select something other than 1-1-0001.

Once another date is selected you can type normally.
Open the drop down calendar and select 1-1-0001 again and the same behavior occurs again.
This bug occurs whether or not ShowCheckBox is true.

Workaround:
- The NullDate should be different that the MinDate

 radDateTimePicker1.NullDate = DateTime.MinValue.AddDays(1);