To reproduce:
- select the whole date and press delete.
- the value should be cleared at this point not when the control loses the focus.

Workaround:

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles Me.Load
        AddHandler RadDateTimePicker1.KeyDown, AddressOf KeyDown_EventHandler
    End Sub

    Private Sub KeyDown_EventHandler(sender As Object, e As KeyEventArgs)
        If e.KeyData = Keys.Delete Then
            e.Handled = True
            RadDateTimePicker1.SetToNullValue()
        End If
    End Sub