RadListBox Scrolling Visual Bug

[Stanislav]

Dear Telerik Team,
We've bumped into next issue. There is RadListBox which exposes CollectionViewSource with grouping.
When user scrolls the listbox up and down (with a mouse wheel or just dragging the thumb), vertical scrollbar changes it's length.
We've ensured that this bug is being reproduced with every Telerik theme set up. And everything is fine if we switch to default WPF ListBox control. 

Here's the code snippet :

<Window x:Class="ListBoxTest.MainWindow"
                xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
                xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
                xmlns:telerik="http://schemas.telerik.com/2008/xaml/presentation"
                Title="MainWindow" Width="1024" Height="768">

    <Window.Resources>
        <CollectionViewSource x:Key="Results" Source="{Binding}">
            <CollectionViewSource.GroupDescriptions>
                <PropertyGroupDescription PropertyName="Category" />
            </CollectionViewSource.GroupDescriptions>
        </CollectionViewSource>
    </Window.Resources>

    <DockPanel DataContext="{Binding}">
        <telerik:RadListBox Margin="0 0 10 10"
                ItemsSource="{Binding Source={StaticResource Results}}"
                SelectedItem="{Binding SelectedItem, Mode=TwoWay}">

            <telerik:RadListBox.GroupStyle>
                <GroupStyle>
                    <GroupStyle.HeaderTemplate>
                        <DataTemplate>
                            <TextBlock Margin="10 10 0 10"
                                        FontWeight="Bold"
                                        Foreground="LightBlue"
                                        Visibility="{Binding Name}"
                                        Text="{Binding Path=Name}"/>
                        </DataTemplate>
                    </GroupStyle.HeaderTemplate>
                </GroupStyle>
            </telerik:RadListBox.GroupStyle>

            <telerik:RadListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel Orientation="Horizontal">
                        <StackPanel Margin="5" VerticalAlignment="Center">
                            <TextBlock FontWeight="Bold"><Run Text="{Binding FirstName, Mode=OneWay}" /> <Run Text="{Binding LastName, Mode=OneWay}" /></TextBlock>
                            <TextBlock>Email: <Run Text="{Binding Email, Mode=OneWay}" /></TextBlock>
                            <TextBlock>Phone: <Run Text="{Binding PhoneNumber, Mode=OneWay}" /></TextBlock>
                        </StackPanel>
                    </StackPanel>
                </DataTemplate>
            </telerik:RadListBox.ItemTemplate>
        </telerik:RadListBox>
    </DockPanel>
</Window>

Is there any way to fix this behavior? Any help will be appreciated.

Best Regards, Stanislav

[Stanislav]

Dear Telerik Team,
The issue described above is an urgent one. 
So it would be brilliant to get some feedback.

Best Regards, Stanislav

[Georgi]

Hi Stanislav,

We are aware of the issue and we have it logged in our Public Issue Tracking System. Here you can vote and track the progress of fixing it, the more votes it gets the more important it becomes to us.
We have tried few things on order to workaround it, but so far we weren't able to do so.
Please, excuse us for the caused inconvenience.

All the best,
Georgi
the Telerik team

[Kay]

For all the others that will get this problem in the future:

From: https://www.telerik.com/forums/vertical-scrollbar-problem-with-one-group

<telerik:RadListBox ScrollViewer.CanContentScroll="False" />