C# 奇怪的 WPF 组合框行为

I have simple window. This is what happens when I click ComboBox: List appears in upper left corner of screen instead of under Combobox.

XAML:

<Window x:Class="WpfPortOfTestingCamera.VideoSettings"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="Video Settings" WindowStartupLocation="CenterOwner" ResizeMode="NoResize" ShowInTaskbar="False" mc:Ignorable="d" xmlns:d="http://schemas.microsoft.com/expression/blend/2008" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" SizeToContent="WidthAndHeight" d:DesignHeight="167">
    <StackPanel Name="stackPanel1" VerticalAlignment="Top" HorizontalAlignment="Center">
        <GroupBox Header="Settings" Name="groupBox1">
            <Grid Name="grid1" VerticalAlignment="Center" HorizontalAlignment="Center">
                <Grid.ColumnDefinitions>
                    <ColumnDefinition Width="80*" />
                    <ColumnDefinition Width="175*" />
                </Grid.ColumnDefinitions>
                <Grid.RowDefinitions>
                    <RowDefinition />
                    <RowDefinition />
                </Grid.RowDefinitions>
                <Label Content="Resolution:" Height="28" Name="label1" Margin="0" HorizontalAlignment="Left" VerticalAlignment="Center" />
                <Label Content="Framerate:" Height="28" HorizontalAlignment="Left" Margin="0" Name="label2" VerticalAlignment="Center" Grid.Row="1" />
                <ComboBox Grid.Column="1" Height="23" HorizontalAlignment="Left" Margin="0" Name="comboBox1" VerticalAlignment="Center" Width="150" SelectionChanged="comboBox1_SelectionChanged" />
                <ComboBox Height="23" HorizontalAlignment="Left" Margin="0" Name="comboBox2" VerticalAlignment="Center" Width="150" Grid.Column="1" Grid.Row="1" SelectionChanged="comboBox2_SelectionChanged" />
            </Grid>
        </GroupBox>
        <Label Name="labelSelectedSize" Content="Size @ FPS" />
        <Button Name="button1" Content="Apply" Click="button1_Click" />
    </StackPanel>
</Window>

不要直接在 Loaded 事件中打开它，只需在 Dispatcher 上排队另一条消息即可打开它。