OK... so this solution doesn't help
XAML is here
<ListBox ItemsSource="{Binding Path=ContentItems}" Background="White" >
<ListBox.ItemTemplate>
<DataTemplate>
<Grid Margin="2" Height="Auto" Width="Auto">
<Grid.ColumnDefinitions>
<ColumnDefinition Width="Auto" />
<ColumnDefinition Width="*" />
</Grid.ColumnDefinitions>
<Grid Grid.Column="0">
<Grid.RowDefinitions>
<RowDefinition Height="Auto"/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<StackPanel Grid.Row="0" Orientation="Horizontal">
<Label VerticalAlignment="Center" Margin="0,0,0,5">Start</Label><svl:TimeEditor Value="{Binding Path=FormatedStart}" Width="87" HorizontalAlignment="Left" Margin="2,8" Name="dtpStart" FontSize="12" Height="25" VerticalAlignment="Center" />
<Label VerticalAlignment="Center" Margin="0,0,0,5">End</Label><svl:TimeEditor Value="{Binding Path=FormatedEnd}" Width="87" HorizontalAlignment="Left" Margin="2,8" Name="dtpEnd" FontSize="12" Height="25" VerticalAlignment="Center" />
</StackPanel>
<TextBlock Grid.Row="1" TextWrapping="Wrap" Name="tbText" Text="{Binding Path=Data}"></TextBlock>
</Grid>
<Grid Grid.Column="1" Visibility="Collapsed">
</Grid>
</Grid>
</DataTemplate>
</ListBox.ItemTemplate>
</ListBox>
Well your TextBlock does not need to wrap since your specifying Width as Auto for it's ColumnDefinition which allows it to take all the Width it needs to fit Content even at the cost of overflowing. You either need to set the Column's Width to "*" to allow the TextWrapping to kick in when requested width exceeds allowable or manually force a MaxWidth on it using a Binding like
<TextBlock Name="tbText" Grid.Row="1" MaxWidth="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type ListBox}}, Path=ActualWidth}" Text="{Binding Path=Data}" TextWrapping="Wrap" />