The problem was in one third party theme I use in my app. That theme has a ListBox
template like:
<Style TargetType="{x:Type ListBox}">
...
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type ListBox}">
<Grid>
<Border x:Name="Border" BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="2" Background="{DynamicResource ControlBackgroundBrush}" />
<ScrollViewer Margin="1" Style="{DynamicResource NuclearScrollViewer}" Focusable="false" Background="{x:Null}">
<StackPanel Margin="1,1,1,1" IsItemsHost="true" />
</ScrollViewer>
</Grid>
<ControlTemplate.Triggers>
<Trigger Property="IsEnabled" Value="false">
<Setter Property="Background" Value="{DynamicResource DisabledBackgroundBrush}" TargetName="Border" />
<Setter Property="BorderBrush" Value="{DynamicResource DisabledBorderBrush}" TargetName="Border" />
</Trigger>
<Trigger Property="IsGrouping" Value="true">
<Setter Property="ScrollViewer.CanContentScroll" Value="false" />
</Trigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
So I use an ItemsPresenter
instead of the StackPanel
in that template and everything works now.