Selected item in a listview doesn't unselect - wpf

Question

I can select multiple items in a listview. But if i click on one, it turns blue. That's normal, so that shows it is selected. But if i click again on the same item, it doesnt uncheck. So i can't change my selection. Somebody who knows how to fix this stupid little problem?
Edit: This is my listview:
<ListView Height="155" ScrollViewer.CanContentScroll="True" ScrollViewer.VerticalScrollBarVisibility="Visible" SelectedItem="{Binding Path=SelectedQuestionDropList, UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}" dd:DragDrop.IsDragSource="True"
dd:DragDrop.IsDropTarget="True" SelectionMode="Multiple" Margin="0,0,542,436" Background="#CDC5CBC5"
dd:DragDrop.DropHandler="{Binding}" Name="DropListView" ItemsSource="{Binding Path=SelectedExaminationQuestions,UpdateSourceTrigger=PropertyChanged,Mode=TwoWay}" SelectionChanged="ListView_SelectionChanged_1" VerticalAlignment="Bottom">
<ListView.View>
<GridView>
<GridView.Columns>
<GridViewColumn Header="Verkorte naam" Width="Auto" DisplayMemberBinding="{Binding Path=ShortName}" />
<GridViewColumn Header="Omschrijving" Width="Auto" DisplayMemberBinding="{Binding Path=Description}" />
<GridViewColumn Header="Type" Width="Auto" DisplayMemberBinding="{Binding Path=Type}" />
</GridView.Columns>
</GridView>
</ListView.View>
</ListView>

Answer 1

I was facing a similar problem and found that, while left-click always select the item pointed to, you can use Ctrl + left-click to toggle selection in a list view. This is the default behavior.

Answer 2

You can write a wpf behaviour. Something like:
public class ListViewBehaviour
{
/// <summary>
/// Enfoca automaticament el item sel·leccionat
/// </summary>
public static readonly DependencyProperty AutoUnselectItemProperty =
DependencyProperty.RegisterAttached(
"AutoUnselect",
typeof(bool),
typeof(ListViewBehaviour),
new UIPropertyMetadata(false, OnAutoUnselectItemChanged));
public static bool GetAutoUnselectItem(ListView listBox)
{
return (bool)listBox.GetValue(AutoUnselectItemProperty);
}
public static void SetAutoUnselectItem(ListView listBox, bool value)
{
listBox.SetValue(AutoUnselectItemProperty, value);
}
private static void OnAutoUnselectItemChanged(DependencyObject source, DependencyPropertyChangedEventArgs e)
{
var listView = source as ListView;
if (listView == null)
return;
if (e.NewValue is bool == false)
listView.SelectionChanged -= OnSelectionChanged;
else
listView.SelectionChanged += OnSelectionChanged;
}
private static void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
{
// TODO write custom selection behaviour
}
}
And to apply it to a listview:
<ListView bb:ListViewBehaviour.AutoUnselect="True">
...
</ListView>