Will be nice to have this feature. I have a solution from support by replacing " with *. But it's the way search should work. Click on link and go to Wildcard *: Searching for Unknown Strings section.
https://www.howtogeek.com/school/learning-windows-search/lesson4/

The workaround is to use a RadTabControl and set its IsContentPreserved to True


Available in LIB version: 2017.2.626

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 };*/
        }

I am setting the status of the item to Declined as the reported behavior is due to the fact that the RowDetailsVisibilityMode is set to VisibleWhenSelected. The default behavior of RadGridView is to split the merged cell when a row with expanded row details is added. Thus, the reported issue you are is the expected one. If setting the RowDetailsVisibilityMode is removed the control will behave as expected. 

Available in LIB version: 2017.2.703

Available in LIB version: 2017.2.724

Current workaround for the affected themes - Define the following control template for the GridViewCheckBox:

			<ControlTemplate x:Key="GridViewCheckBoxTemplate" TargetType="telerik:GridViewCheckBox">
				<Grid HorizontalAlignment="Left" VerticalAlignment="Center" Width="13" Height="13">
					<VisualStateManager.VisualStateGroups>
						<VisualStateGroup x:Name="CheckStates">
							<VisualState x:Name="Checked">
								<Storyboard>
									<ObjectAnimationUsingKeyFrames BeginTime="0" Duration="0" Storyboard.TargetName="CheckedPath" Storyboard.TargetProperty="(UIElement.Visibility)">
										<DiscreteObjectKeyFrame KeyTime="0">
											<DiscreteObjectKeyFrame.Value>
												<Visibility>Visible</Visibility>
											</DiscreteObjectKeyFrame.Value>
										</DiscreteObjectKeyFrame>
									</ObjectAnimationUsingKeyFrames>
								</Storyboard>
							</VisualState>
							<VisualState x:Name="Unchecked"/>
							<VisualState x:Name="Indeterminate">
								<Storyboard>
									<ObjectAnimationUsingKeyFrames BeginTime="0" Duration="0" Storyboard.TargetName="IndeterminatePath" Storyboard.TargetProperty="(UIElement.Visibility)">
										<DiscreteObjectKeyFrame KeyTime="0">
											<DiscreteObjectKeyFrame.Value>
												<Visibility>Visible</Visibility>
											</DiscreteObjectKeyFrame.Value>
										</DiscreteObjectKeyFrame>
									</ObjectAnimationUsingKeyFrames>
								</Storyboard>
							</VisualState>
						</VisualStateGroup>
					</VisualStateManager.VisualStateGroups>
					<Grid Background="Transparent">
						<Border
                        BorderBrush="{TemplateBinding BorderBrush}"
                        Background="{TemplateBinding Background}"
                        BorderThickness="{TemplateBinding BorderThickness}"
                        CornerRadius="{telerik:Office2016Resource ResourceKey=CornerRadius}"/>
						<Border x:Name="IndeterminatePath"
                        Width="9"
                        Height="9"
                        VerticalAlignment="Center"
                        HorizontalAlignment="Center"
                        Background="{telerik:Office2016Resource ResourceKey=IconBrush}"
                        Visibility="Collapsed"/>
						<TextBlock x:Name="CheckedPath"
                        HorizontalAlignment="Center"
                        VerticalAlignment="Center"
                        FontSize="13"
                        FontWeight="Normal"
                        FontStyle="Normal"
                        Foreground="{TemplateBinding Foreground}"
                        FontFamily="{StaticResource TelerikWebUI}"
                        telerik:GlyphAdorner.ShowGlyphInDesignTime="True"
                        Opacity="1"
                        Margin="-1 0 0 0"
                        Visibility="Collapsed">
                    <Run Text="{StaticResource GlyphCheck}"/>
						</TextBlock>
					</Grid>
				</Grid>
			</ControlTemplate>
			<Style  TargetType="telerik:GridViewCheckBox" BasedOn="{StaticResource GridViewCheckBoxStyle}">
				<Setter Property="Template" Value="{StaticResource GridViewCheckBoxTemplate}"/>
			</Style>

Fix available in LIB version 2017.2.814.

In Office2016 when we increase the DPI of the Windows a left border in the header of column disappears. As a workaround you can set the Width property of all columns.

Currently, if the value set to the RowHeight of RadGridView is lower than the Height of the highest cell(or the Height of a Hierarchy defined), it will not be respected. Provide an option the RowHeight to have greater weight than the height of the cell.

When we make frozen column width bigger than the window will hide other columns. Scrolling is applied only to not frozen columns. So we can't scroll to see other columns.

A possible workaround is to set MaxWidth property of the column.

Currently VQCV caches all the items once they are loaded. In this way the data virtaulization functions only through the first bottom-most item scrolling. The idea behind this item is to make this behavior optional by introducing an alternative mode.

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

Edit:
We are declining this bug as originally the export options were not meant to respect group properties but only some global GridView properties.
However we will add such option in GridViewDocumentExportOptions class.
You can follow this feature request => 
https://feedback.telerik.com/Project/143/Feedback/Details/229211-gridview-add-option-in-gridviewdocumentexportoptions-to-include-exclude-grouph

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);
		}
	}
}

Add option in GridViewDocumentExportOptions to include / exclude GroupHeaderRowAggregates.

This will allow users to hide/show group header row aggregates in the exported documents.

Option will be globbally applied - to all group header rows in the RadGridView.
===
From 2017 R3 SP GridViewDocumentExportOptions  adds ShowGroupHeaderRowAggregates bool property.

It can be used like so:

  GridViewDocumentExportOptions options = new GridViewDocumentExportOptions()
            {
                ShowGroupHeaderRowAggregates = true
            };
this.gridView.ExportToWorkbook(options);

Currently, you can use only the predefined one - IsEqual, IsNotEqual, etc. Add an option to create operators that execute custom filtering action. Also, add support for modifying the default operators.