As a workaround, the Path with the PathGeometry setter in the style can be replaced by a RadGlyph with a pin icon. The IsPinned Trigger in the style can be replaced with a DataTrigger to the parent row's IsPinned. Here's an example of the updated style for the Fluent theme:

<Style x:Key="GridViewPinButtonStyle" TargetType="grid:GridViewPinButton">
        <Setter Property="PathStyle" Value="{StaticResource PinUnpinPathStyle}"/>
        <Setter Property="Foreground" Value="{telerik1:FluentResource ResourceKey=IconBrush}"/>
        <Setter Property="MinHeight" Value="28"/>
        <Setter Property="MinWidth" Value="22"/>
        <Setter Property="IsBackgroundVisible" Value="False"/>
        <Setter Property="Command" Value="{x:Static telerik:RadGridViewCommands.TogglePinnedRowState}"/>
        <Setter Property="CommandParameter" Value="{Binding}"/>
        <Setter Property="SnapsToDevicePixels" Value="True"/>
        <Setter Property="BorderThickness" Value="0"/>
        <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
        <Setter Property="VerticalContentAlignment" Value="Stretch"/>
        <Setter Property="FocusVisualStyle" Value="{x:Null}"/>
        <Setter Property="IsTabStop" Value="False"/>
        <Setter Property="Padding" Value="0 0 2 0"/>
        <Setter Property="Template">
            <Setter.Value>
                <ControlTemplate TargetType="telerik:RadPathButton">
                    <Grid Background="Transparent">
                        <VisualStateManager.VisualStateGroups>
                            <VisualStateGroup x:Name="BackgroundVisibility">
                                <VisualState x:Name="BackgroundIsHidden">
                                    <Storyboard>
                                        <ObjectAnimationUsingKeyFrames Storyboard.TargetName="OuterBorder" Storyboard.TargetProperty="Visibility">
                                            <DiscreteObjectKeyFrame KeyTime="0">
                                                <DiscreteObjectKeyFrame.Value>
                                                    <Visibility>Collapsed</Visibility>
                                                </DiscreteObjectKeyFrame.Value>
                                            </DiscreteObjectKeyFrame>
                                        </ObjectAnimationUsingKeyFrames>
                                    </Storyboard>
                                </VisualState>
                                <VisualState x:Name="BackgroundIsVisible"/>
                            </VisualStateGroup>
                        </VisualStateManager.VisualStateGroups>
                        <Border x:Name="OuterBorder"
                                BorderThickness="{TemplateBinding BorderThickness}"
                                BorderBrush="{TemplateBinding BorderBrush}"
                                Background="{TemplateBinding Background}"
                                CornerRadius="{TemplateBinding CornerRadius}"/>
                        <telerik:RadGlyph x:Name="UnPinIcon" Foreground="{TemplateBinding Foreground}" FontSize="16" HorizontalAlignment="Center" VerticalAlignment="Center" Glyph="{StaticResource GlyphPin}"/>
                    </Grid>
                    <ControlTemplate.Triggers>
                        <Trigger Property="IsMouseOver" Value="True">
                            <Setter Property="Foreground" Value="{telerik1:FluentResource ResourceKey=AccentMouseOverBrush}"/>
                        </Trigger>
                        <Trigger Property="IsPressed" Value="True">
                            <Setter Property="Foreground" Value="{telerik1:FluentResource ResourceKey=AccentPressedBrush}"/>
                        </Trigger>
                        <DataTrigger Binding="{Binding IsPinned, RelativeSource={RelativeSource AncestorType=telerik:GridViewRow}}" Value="True">
                            <Setter TargetName="UnPinIcon" Property="Glyph" Value="{StaticResource GlyphUnpin}" />
                        </DataTrigger>
                    </ControlTemplate.Triggers>
                </ControlTemplate>
            </Setter.Value>
        </Setter>
    </Style>

ArgumentException: 'RadGlyphExtension' is not valid for Setter.Value. The only supported MarkupExtension types are DynamicResourceExtension and BindingBase or derived types.

StackTrace:
   at System.Windows.Setter.Seal()
   at System.Windows.SetterBaseCollection.Seal()
   at System.Windows.Style.Seal()
   at System.Windows.Style.Seal()
   at System.Windows.StyleHelper.UpdateStyleCache(FrameworkElement fe, FrameworkContentElement fce, Style oldStyle, Style newStyle, Style& styleCache)
   at System.Windows.FrameworkElement.OnStyleChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
   at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
   at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
   at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
   at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
   at System.Windows.DependencyObject.InvalidateProperty(DependencyProperty dp, Boolean preserveCurrentValue)
   at System.Windows.FrameworkElement.UpdateStyleProperty()
   at System.Windows.FrameworkElement.OnInitialized(EventArgs e)
   at Telerik.Windows.Controls.RadButton.OnInitialized(EventArgs e)
   at Telerik.Windows.Controls.RadPathButton.OnInitialized(EventArgs e)
   at Telerik.Windows.Controls.GridView.GridViewPinButton.OnInitialized(EventArgs e)
   at System.Windows.FrameworkElement.TryFireInitialized()
   at System.Windows.FrameworkElement.EndInit()
   at MS.Internal.Xaml.Runtime.ClrObjectRuntime.InitializationGuard(XamlType xamlType, Object obj, Boolean begin)

Setting the theme via the StyleManager.SetTheme(control, theme) method does not style the cell as expected when a CellStyle is defined for its parent column.

The current workaround is to explicitly set the theme via the style:
<Style x:Key="BlueCellStyle" TargetType="telerik:GridViewCell">
		<Setter Property="Background" Value="PowderBlue"/>
                <Setter Property="telerik:StyleManager.Theme" Value="VisualStudio2013" />
</Style>

To work this around set the GroupRenderMode property of RadGridView to Flat.

When GroupRenderMode is set to Nested the issue can be overcome by calling the BringIntoView method on the row returned in the ScrollIntoViewAsync method's callback:  
gridView.ScrollIndexIntoViewAsync(index,
  new Action<FrameworkElement>((f) =>
  {
      f.BringIntoView();
  }));

If you have a RadComboBox inside a ControlPanelItem, when you open the RadComboBox's dropdown and select an item, the ControlPanelItem is not closed. As a workaround, you can manually capture the mouse. Please check the attached project.

When setting the VirtualItemCount on refreshing the data source, the scrollbar jumps to the top. If the VirtualItemCount is initially set, the behavior is not reproduced. The workaround is to use the scrolling mechanism of the control and scroll back to the desired item.

Currently, the following workaround can be applied:

private void RadGridView_Loaded(object sender, RoutedEventArgs e)
{
	var gridView = sender as RadGridView;
	foreach (var column in gridView.Columns)
	{
		if (!column.IsResizable)
		{
			Dispatcher.BeginInvoke((Action) (() =>
			{
				var radGridView = column.Parent;
				foreach (var header in radGridView.ChildrenOfType<GridViewHeaderCell>())
				{
					if (header.Column.DisplayIndex == column.DisplayIndex)
					{
						var leftGripper = header.ChildrenOfType<Thumb>().Where(x => x.Name == "PART_LeftHeaderGripper").First();
						{
							leftGripper.Visibility = Visibility.Collapsed;
						}
					}
					else if (header.Column.DisplayIndex == (column.DisplayIndex - 1))
					{
						var rightGripper = header.ChildrenOfType<Thumb>().Where(x => x.Name == "PART_RightHeaderGripper").First();
						{
							rightGripper.Visibility = Visibility.Collapsed;
						}
					}
				}
			}), DispatcherPriority.Render);
		}
	}
}

This is reproducible in a hierarchical scenario. The nested gridview loses its selection when its parent row is scrolled out of the viewport.

workaround:
public MainWindow()
{
    InitializeComponent();

    this.grid.Loaded += grid_Loaded;
}

void grid_Loaded(object sender, RoutedEventArgs e)
{
    this.grid.ChildrenOfType<Grid>().FirstOrDefault(x => x.Name == "PART_OuterGrid").RowDefinitions[1].Height = GridLength.Auto;

    var cells = this.grid.ChildrenOfType<GridViewHeaderCell>();
    foreach (GridViewHeaderCell cell in cells)
    {
        cell.ChildrenOfType<Grid>().FirstOrDefault(x => x.Name == "PART_OuterGrid").RowDefinitions[1].Height = GridLength.Auto;
    }
}

To work this around you can set the EnableColumnGroupsVirtualization to False.

Alternatively you can change the FrozenColumnCount before adding the columns, and reset it once the process is done. For example:

gridTriffDetails.FrozenColumnCount = 0;
 
gridTriffDetails.Columns.Add(newColumn);
gridTriffDetails.Columns.Add(newColumn1);
gridTriffDetails.Columns.Add(newColumn2);
 
gridTriffDetails.FrozenColumnCount = 1;

workaround is to override the OnInitialized of the custom column:

 protected override void OnInitialized(EventArgs e)
        {/* //if XAML assemblies

            Theme theme = StyleManager.GetTheme(this);
            Type themeType = null;
            if (theme != null)
            {
                themeType = theme.GetType();
            }
            this.DefaultStyleKey = new ThemeResourceKey() { ElementType = typeof(Telerik.Windows.Controls.GridViewColumn), ThemeType = themeType };*/
        }