The expanded state of the hierarchical item is not preserved when searching thought search panel for something that is not found and clearing search text.

When you define a style targeted at GridViewCell with a color without transparency, horizontal grid lines are hidden.

If you set BorderThickness through a custom CellStyle, the left border is overwritten by our code. 

Full error message: No generic method 'Sum' on type 'System.Linq.Enumerable' is compatible with the supplied type arguments and arguments. No type arguments should be provided if the method is non-generic."

Showing in design time, working at run time. 

Placing text in quotes after exclude search operator and search getting the wrong result. As a workaround to get the desired result the search string can be changed in this way: from  -"Rio de" to  -Rio + -de.

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();
  }));

An implicit style could be added:

<Style TargetType="telerik:FilteringControl" BasedOn="{StaticResource FilteringControlStyle}">
   <Setter Property="Background" Value="{telerik:FluentResource ResourceKey=AlternativeBrush}" />
</Style>

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.