WindowsFormsHost ToolTipService

Question

我遇到的问题的简单案例代码：

<Window x:Class="WFHTooltipEnableTest.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:wf="clr-namespace:System.Windows.Forms;assembly=System.Windows.Forms"  
    >
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition></RowDefinition>
            <RowDefinition></RowDefinition>                        
        </Grid.RowDefinitions>
        <WindowsFormsHost Name="HostControl">
            <wf:MaskedTextBox x:Name="mtbDate" Mask="00/00/0000"/>
        </WindowsFormsHost>
        <Button Content="Toggle" Grid.Row="1" Click="Button_Click"></Button>
    </Grid>
</Window>

using System.Windows;
using System.Windows.Controls;

namespace WFHTooltipEnableTest
{
    public partial class MainWindow : Window
    {
        bool enabled = true;
        public MainWindow() {}
        private void Button_Click(object sender, RoutedEventArgs e)
        {
            enabled = !enabled;
            ToolTipService.SetIsEnabled(this.HostControl, enabled);
        }
    }
}

该按钮将切换传递给SetIsEnabled的值。如果为false，则窗体主机控件中托管的内容将被禁用。

似乎无法找到此行为的任何解释。