I'm using UXStackButton and it does not work properly for RightToLeft cultures. The popup is positioned partial or totally off the screen.

Here's a test page:

<Intersoft:UXPage 
	xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
	xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
	xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
	xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
	mc:Ignorable="d"
	xmlns:Intersoft="http://intersoft.clientui.com/schemas"
	x:Class="test1.MainPage" 
	Title="MainPage Page"
	d:DesignWidth="463" d:DesignHeight="383">
	
	<Grid x:Name="LayoutRoot" FlowDirection="RightToLeft">
        <Intersoft:UXStackButton Content="Button" DisplayMode="Content" 
                                 HorizontalContentAlignment="Center" VerticalContentAlignment="Center"
                                 StackDockPosition="Top" HorizontalAlignment="Center" VerticalAlignment="Top" 
                                 Height="64" Width="64"  StackMode="GridStyle">
            <Intersoft:UXStackButton.StackGridTemplate>
                <DataTemplate>
                    <Grid Width="400">
                        <Grid.RowDefinitions>
                            <RowDefinition />
                            <RowDefinition />
                        </Grid.RowDefinitions>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition  />
                            <ColumnDefinition />
                        </Grid.ColumnDefinitions>
                        <Intersoft:FieldLabel HeaderForeground="White" Header="Label1" Margin="4" Grid.Column="0" Grid.Row="0" />
                        <Intersoft:UXTextBox Margin="4" Grid.Column="1" Grid.Row="0" />
                        <Intersoft:FieldLabel HeaderForeground="White" Header="Label1" Margin="4" Grid.Column="0" Grid.Row="1" />
                        <Intersoft:UXTextBox  Margin="4" Grid.Column="1" Grid.Row="1" />
                    </Grid>
                </DataTemplate>
            </Intersoft:UXStackButton.StackGridTemplate>            
        </Intersoft:UXStackButton>
        <Intersoft:UXStackButton Content="Button" DisplayMode="Content" 
                                 HorizontalContentAlignment="Center" VerticalContentAlignment="Center"
                                 StackDockPosition="Top" HorizontalAlignment="Center" VerticalAlignment="Bottom" 
                                 Height="64" Width="64"  StackMode="GridStyle">
            <Intersoft:UXStackButton.StackGridTemplate>
                <DataTemplate>
                    <Grid Width="400">
                        <Grid.RowDefinitions>
                            <RowDefinition />
                            <RowDefinition />
                        </Grid.RowDefinitions>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition  />
                            <ColumnDefinition />
                        </Grid.ColumnDefinitions>
                        <Intersoft:FieldLabel HeaderForeground="White" Header="Label1" Margin="4" Grid.Column="0" Grid.Row="0" />
                        <Intersoft:UXTextBox Margin="4" Grid.Column="1" Grid.Row="0" />
                        <Intersoft:FieldLabel HeaderForeground="White" Header="Label1" Margin="4" Grid.Column="0" Grid.Row="1" />
                        <Intersoft:UXTextBox  Margin="4" Grid.Column="1" Grid.Row="1" />
                    </Grid>
                </DataTemplate>
            </Intersoft:UXStackButton.StackGridTemplate>
        </Intersoft:UXStackButton>
        <Intersoft:UXStackButton Content="Button" DisplayMode="Content" 
                                 HorizontalContentAlignment="Center" VerticalContentAlignment="Center"
                                 StackDockPosition="Top" HorizontalAlignment="Left" VerticalAlignment="Center" 
                                 Height="64" Width="64" StackMode="GridStyle">
            <Intersoft:UXStackButton.StackGridTemplate>
                <DataTemplate>
                    <Grid Width="400">
                        <Grid.RowDefinitions>
                            <RowDefinition />
                            <RowDefinition />
                        </Grid.RowDefinitions>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition  />
                            <ColumnDefinition />
                        </Grid.ColumnDefinitions>
                        <Intersoft:FieldLabel HeaderForeground="White" Header="Label1" Margin="4" Grid.Column="0" Grid.Row="0" />
                        <Intersoft:UXTextBox Margin="4" Grid.Column="1" Grid.Row="0" />
                        <Intersoft:FieldLabel HeaderForeground="White" Header="Label1" Margin="4" Grid.Column="0" Grid.Row="1" />
                        <Intersoft:UXTextBox  Margin="4" Grid.Column="1" Grid.Row="1" />
                    </Grid>
                </DataTemplate>
            </Intersoft:UXStackButton.StackGridTemplate>
        </Intersoft:UXStackButton>
        <Intersoft:UXStackButton Content="Button" DisplayMode="Content" 
                                 HorizontalContentAlignment="Center" VerticalContentAlignment="Center"
                                 StackDockPosition="Top" HorizontalAlignment="Right" VerticalAlignment="Center" 
                                 Height="64" Width="64" StackMode="GridStyle">
            <Intersoft:UXStackButton.StackGridTemplate>
                <DataTemplate>
                    <Grid Width="400">
                        <Grid.RowDefinitions>
                            <RowDefinition />
                            <RowDefinition />
                        </Grid.RowDefinitions>
                        <Grid.ColumnDefinitions>
                            <ColumnDefinition  />
                            <ColumnDefinition />
                        </Grid.ColumnDefinitions>
                        <Intersoft:FieldLabel HeaderForeground="White" Header="Label1" Margin="4" Grid.Column="0" Grid.Row="0" />
                        <Intersoft:UXTextBox Margin="4" Grid.Column="1" Grid.Row="0" />
                        <Intersoft:FieldLabel HeaderForeground="White" Header="Label1" Margin="4" Grid.Column="0" Grid.Row="1" />
                        <Intersoft:UXTextBox  Margin="4" Grid.Column="1" Grid.Row="1" />
                    </Grid>
                </DataTemplate>
            </Intersoft:UXStackButton.StackGridTemplate>
        </Intersoft:UXStackButton>
    </Grid>
</Intersoft:UXPage>

 For LeftToRight FlowDirection it is working ok.

I'm using the latest update ClientUI5_0_5000_4 for SIlverlight 4.