DateTimePicker binding overwrites time

<Window x:Class="WpfApplication1.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:shared="http://schemas.actiprosoftware.com/winfx/xaml/shared"
    xmlns:l="clr-namespace:WpfApplication1"
    Title="Window1" Height="300" Width="300">
    <Window.Resources>
        <l:BoundObject x:Key="boundObject"/>
    </Window.Resources>
    <Grid DataContext="{StaticResource boundObject}">
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"/>
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition Width=".5*"/>
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition Width=".5*"/>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>
        <shared:DateTimePicker Grid.Column="0" Value="{Binding Path=DateTime}"/>
        <TextBlock Grid.Column="1" Text="Hour:"/>
        <TextBlock Grid.Column="2" Text="{Binding Path=DateTime.Hour}"/>
        <TextBlock Grid.Column="3" Text="Minute:"/>
        <TextBlock Grid.Column="4" Text="{Binding Path=DateTime.Minute}"/>
    </Grid>
</Window>

using System;
using System.ComponentModel;

namespace WpfApplication1
{
    public class BoundObject : INotifyPropertyChanged
    {
        private DateTime _dateTime;
        public BoundObject()
        {
            _dateTime = DateTime.Now;
        }

        public DateTime DateTime
        {
            get { return _dateTime; }
            set { _dateTime = value; NotifyPropertyChanged("DateTime"); }
        }

        #region INotifyPropertyChanged Members
        public event PropertyChangedEventHandler PropertyChanged;

        private void NotifyPropertyChanged(string propertyName)
        {
            if (PropertyChanged != null)
            {
                PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
            }
        }
        #endregion
    }
}