DateTimeEditBox clock window closing problem

Please use folowing code to repro a bug:

<Window x:Class="WpfApplication2.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:editors="http://schemas.actiprosoftware.com/winfx/xaml/editors"
ResizeMode="NoResize"
SizeToContent="WidthAndHeight"
WindowStartupLocation="CenterOwner"
MaxWidth="450"
MinWidth="450"
Background="{DynamicResource ResourceKey={x:Static SystemColors.ControlBrushKey}}"
Foreground="{x:Static SystemColors.WindowTextBrush}"
x:Name="_win">
<Grid>
<editors:DateTimeEditBox
CheckBoxVisibility="Visible"
SpinnerVisibility="Visible"
HorizontalAlignment="Left"
Format="t"
IsReadOnly="False"
/>
</Grid>
</Window>

It is impossible to close "Clock" component with [X] button, because of [X] button inaccessibility.

Issue do not uccures when we use another format string (for example "g" ).

Build 11.2.552.0 used.