Currently the column virtualization is disabled in column groups view, which causes slow scrolling when using a large number of columns

The GroupRow Height cannot be changed when ColumnGroupsViewDefinition and HtmlViewDefinition are used.

The issue appears when the ViewDefinition of the control is ColumnGroupsViewDefinition, summary rows are added and grouping is performed.

If you create conditional formatting, the rows that obey the rule should not be affected if they are selected.
To support this formatting the format.ApplyOnSelectedRows property must be set to false.
Test project:
using System.Data;
using System.Drawing;
using System.Windows.Forms;
using Telerik.WinControls.UI;
namespace Lab.Grid
{
public partial class GridConditionalFormattingForm : Form
{
private RadGridView gridView = new RadGridView();
public GridConditionalFormattingForm()
{
InitializeComponent();
gridView.Dock = DockStyle.Fill;
gridView.Parent = this;
gridView.MultiSelect = true;
DataTable data = new DataTable();
data.Columns.Add("ID");
data.Columns.Add("Name");
data.Rows.Add(1, "Name1");
data.Rows.Add(2, "Name2");
data.Rows.Add(1, "Name3");
data.Rows.Add(4, "Name4");
data.Rows.Add(1, "Name5");
gridView.DataSource = data;
}
protected override void OnLoad(System.EventArgs e)
{
base.OnLoad(e);
ConditionalFormattingObject format = new ConditionalFormattingObject("MyCondition", ConditionTypes.Equal, "1", "", true);
format.CellBackColor = Color.Red;
format.ApplyOnSelectedRows = false;
gridView.Columns[0].ConditionalFormattingObjectList.Add(format);
}
}
}

related to fitering functionality of RadGridView control
Comment: 
Refreshing the master template of RadGridView in the CellEndEdit event handler is not allowed from the current architecture of the control. Use radGridView1.TableElement.Update(GridUINotifyAction.DataChanged) instead.

The AlternatingRowColor value is restarted when the ViewDefinition is changed.

When canceling the CurrentRowChanging event and the changing row is the new row, then the click here to add new row text will not be visible anymore.

Replacing the RadTextBoxItem with RadTextBoxElement in the RadGridView editor will provide richer theming capabilities.

If you change the values of the other business objects, when one of them is changed, RadGridView's rows' values are not affected.

The issue occurs when using a BindingSource bound to a DataSet as DataSource for combo box columns in RadGridView.

RadGridView does not clear the GridSpinEditor value when navigating to another cell.

RadGridView. Incorrect behavior of arrow keys when RightToLeft is enabled.

Save\Load functionality of the control should work with ColumnGroupsViewDefinition.

When switching from a child view that does not contain rows to one containing rows, the child view size is not updated and no child rows are shown.

If you go to The Demos >> Grid View >> Performance >> Load 50,000 rows. And then drag the group to group by the first two columns, then editing cells is slow.

RadGridView can not change the current column (by using the IsCurrent of the desired column) in the CurrentColumnChanged event.

The issue may be releated to measure layout logic.

Ticked ID: 381352
One thing more I noticed.
Actually I do not think, this issue is a sorting issue, but rather some rendering issue, where the old version is much faster than the new one. 
If you compare the scrolling performance between the new and the old version, also here the old version is significantly faster.
So I think this is a more general issue, something with the rendering - or what you call it - of the visible part of the grid, which are faster in the old version.
Am I the only customer noticing this ?

steps to reproduce: 

1- Apply filter in a date column by choosing Between. 

2- Leave default settings (change dates) and confirm 

3- Save layout 

4- Close the form 

5- Open the form and load the layout 

forum: http://www.telerik.com/community/forums/winforms/gridview/save-load-layout-issue.aspx#1475412 

RadGridView does not handle nullable DateTime objects correctly.

IIF function in Expression for calculated columns does not work.