Silverlight Accordion doesn't resize - xaml

Question

I have an incredible annoying problem with accordion content template.
It shows perfectly, no problem with databinding or something else, but when i resize the browser window the tabControl inside the detail of the accordion doesn't resize at all.
It seems like the width is fixed but acctually it's not.
When the listbox has to change data because of the databinding, the tabcontrol resize perfectly to the new browser window size. Any suggestions please?
My code is:
<layoutToolkit:Accordion.ContentTemplate>
<DataTemplate>
<!--#Sinergia Wave2-->
<Grid>
<sdk:TabControl Grid.Row="1" Grid.ColumnSpan="4" Loaded="ListBox_Loaded" SizeChanged="ListaDetailControlli_SizeChanged">
<sdk:TabItem Header="Controlli">
<Grid Visibility="{Binding HasItems, Converter={StaticResource ConvertBooleanToVisible}}">
<Grid.RowDefinitions>
<RowDefinition Height="auto" />
<RowDefinition Height="auto" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="10" />
<ColumnDefinition Width="300" />
<!--Colonna del semaforo -->
<ColumnDefinition Width="44" />
<ColumnDefinition Width="300*" />
</Grid.ColumnDefinitions>
<StackPanel Grid.Row="0" Grid.ColumnSpan="4" Orientation="Horizontal">
<Grid SizeChanged="Grid_SizeChanged" Background="#FFC1C1C1" Height="25">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="10" />
<ColumnDefinition Width="300" />
<!--Colonna del semaforo -->
<ColumnDefinition Width="44" />
<ColumnDefinition Width="300*" />
</Grid.ColumnDefinitions>
<dataInput:Label Grid.Column="1" FontSize="12" FontWeight="Bold" Content="Controllo" HorizontalAlignment="Left" VerticalAlignment="Center" />
<dataInput:Label Grid.Column="3" FontSize="12" FontWeight="Bold" Content="Dettagli" HorizontalAlignment="Left" VerticalAlignment="Center" />
</Grid>
</StackPanel>
<ListBox Name="ListaDetailControlli" BorderThickness="0" Grid.Row="1" Grid.ColumnSpan="4" ItemsSource="{Binding ListaControlli}" SelectionMode="Single"
SelectedItem="{Binding SelectedTask, Mode=TwoWay}" ScrollViewer.HorizontalScrollBarVisibility="Disabled" ScrollViewer.VerticalScrollBarVisibility="Auto">
<ListBox.ItemTemplate>
<DataTemplate>
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="22" />
</Grid.RowDefinitions>
<Grid.ColumnDefinitions>
<ColumnDefinition Width="300" />
<ColumnDefinition Width="44" />
<ColumnDefinition Width="300*" />
</Grid.ColumnDefinitions>
<TextBlock Grid.Column="0" FontSize="10" Margin="2,0,4,0" VerticalAlignment="Center" HorizontalAlignment="Stretch" TextAlignment="Left"
Text="{Binding DescrizioneControllo}" />
<Canvas Grid.Column="1"
Width="22"
Height="22"
Margin="0,0,4,0">
<Image Source="/Image/Traffic-no-light.png"
Width="22"
Height="22"
Margin="0,0,4,0" />
<Ellipse Canvas.Left="7"
Canvas.Top="2"
Width="8"
Height="8"
Fill="{Binding ColoreControllo}" />
<Ellipse Canvas.Left="7"
Canvas.Top="11"
Width="8"
Height="8"
Fill="{Binding ColoreControllo}" />
</Canvas>
<!-- #135162;dv;; Pannello Controlli -->
<TextBlock Grid.Column="2" FontSize="10" Margin="2,0,4,0" TextAlignment="Left" Text="{Binding DettaglioControllo}" />
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</Grid>
</sdk:TabItem>
<sdk:TabItem Header="Task" GotFocus="TabTask_GotFocus">
<Grid VerticalAlignment="Stretch">
<Border BorderThickness="0" VerticalAlignment="Center" HorizontalAlignment="Center">
<TextBlock Foreground="Red" FontSize="18" FontWeight="Bold" Text="Non è presente nessun task per il giorno selezionato" TextWrapping="Wrap"
Visibility="{Binding Path=HasTask, Converter={StaticResource ConvertBooleanToVisibleNegato}}" />
</Border>
<ScrollViewer BorderThickness="0" Visibility="{Binding Path=HasTask, Converter={StaticResource ConvertBooleanToVisible}}">
<ListBox x:Name="ListaTask" BorderThickness="0" Tag="{Binding ID_SERBATOIO}" MinWidth="250" Margin="-2,-1,-2,0" HorizontalAlignment="Stretch"
ItemContainerStyle="{StaticResource CheckBoxItemContainerStyleWithStatusDiari}" ItemsSource="{Binding ListaTask}"
ScrollViewer.HorizontalScrollBarVisibility="Disabled">
<ListBox.ItemTemplate>
<DataTemplate>
<StackPanel Orientation="Horizontal" Margin="0">
<StackPanel>
<Border x:Name="BorderDrop" Height="20" Margin="8,0,0,0" Background="Gray" BorderThickness="4" Canvas.ZIndex="-2" CornerRadius="9"
Opacity="0.8" Padding="0" Visibility="Collapsed">
<Border.BorderBrush>
<LinearGradientBrush StartPoint="0.5,0" EndPoint="0.5,1">
<GradientStop Offset="0.2" Color="Black" />
<GradientStop Offset="0.8" Color="#FFCDCCCC" />
</LinearGradientBrush>
</Border.BorderBrush>
</Border>
<controlsLIB:TaskMultiTemp DataContext="{Binding }" PannelloOspitante="{Binding LayoutOspitante,ElementName=panValidazioneOperatori,
Mode=OneWay}"
TemplateTipo="{Binding TemplateMultiTemp,ElementName=panValidazioneOperatori,Mode=OneWay}" />
</StackPanel>
</StackPanel>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
</ScrollViewer>
</Grid>
</sdk:TabItem>
</sdk:TabControl>
</Grid>
</DataTemplate>