Monogame WinPhone 8.1 with xaml elements

Windows Phone
1

Hi! I Create monogame project for wp8.1, but i cann’t add sub element for SwapChainBackgroundPanel, they just are not displayed.
Simple:

Xaml:

<SwapChainBackgroundPanel
    x:Class="Game1.GamePage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="using:Game1"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d">

    <Grid>
        <Button Content="THIS IS THE TEST BUTTON" Background="Red" HorizontalAlignment="Center"/>
    </Grid>
</SwapChainBackgroundPanel>

C#:

public sealed partial class GamePage : SwapChainBackgroundPanel
{
    readonly Game1 _game;
    public GamePage()
    {
        this.InitializeComponent();
    }

    public GamePage(string launchArguments)
    {
        _game = XamlGame<Game1>.Create(launchArguments, Window.Current.CoreWindow, this);
    }
}

Button not show. How to solve this problem?