Export to excel fails when there is null values for GridViewDateTimeColumn.
The following code snippet reproduce the issue:

ExportToExcelML export = new ExportToExcelML(gridView);
export.HiddenColumnOption = HiddenOption.DoNotExport;
export.HiddenRowOption = HiddenOption.DoNotExport;
export.ExportVisualSettings = false;
export.SheetMaxRows = ExcelMaxRows._1048576;
export.RunExport(targetFileName);

Filtering does not work correctly when NotConains and Contains filters are combined.

Work around:

private void radGridView1_FilterExpressionChanged(object sender, FilterExpressionChangedEventArgs e)
        {
            List<string> filterExpressions = new List<string>();

            for (int i = 0; i < this.radGridView1.FilterDescriptors.Count; i++)
            {
                FilterDescriptor descriptor = this.radGridView1.FilterDescriptors[i];
                string expression = null;

                CompositeFilterDescriptor compositeFilterDescriptor = descriptor as CompositeFilterDescriptor;

                if (compositeFilterDescriptor != null)
                {

                    expression = CompositeFilterDescriptor.GetCompositeExpression(compositeFilterDescriptor);
                }
                else
                {
                    expression = FilterDescriptor.GetExpression(descriptor);
                }

                if (!string.IsNullOrEmpty(expression))
                {
                    filterExpressions.Add("(" + expression + ")");
                }
            }

            string logicalOperator = (this.radGridView1.FilterDescriptors.LogicalOperator == FilterLogicalOperator.And) ? " AND " : " OR ";
            string resultExpression = String.Join(logicalOperator, filterExpressions.ToArray());
            e.FilterExpression = resultExpression;
        }

The display member for empty string value in GridViewComboBoxColumn is not displayed. The following code reproduces the issue:

GridViewComboBoxColumn cboInsRslCd = new GridViewComboBoxColumn();
cboInsRslCd.DataType = typeof(string);
List<ItemComboBox> liste = new List<ItemComboBox>();
liste.Add(new ItemComboBox("", "[None]"));
liste.Add(new ItemComboBox("A", "A"));
liste.Add(new ItemComboBox("B", "B"));
liste.Add(new ItemComboBox("C", "C"));

cboInsRslCd.DataSource = liste;
cboInsRslCd.ValueMember = "CleItem";
cboInsRslCd.DisplayMember = "ValeurItem";
cboInsRslCd.NullValue = "[None]";
this.radGridView1.Columns.Add(cboInsRslCd);

WORKAROUND:  subscribe to the CellEndEdit event and change the stored value in the event handler:
private void RadGridView1_CellEndEdit(object sender, GridViewCellEventArgs e)
{
    if (e.Value == null)
    {
        e.Row.Cells[e.Column.Name].Value = "";
    }
}

http://www.telerik.com/community/forums/radgridview-comboboxcolumn-displays-no-value-for-member-with-empty-string-value-is-selected

Object-hierarchy produces same child rows for every parent row.

Scrolling when column reorder is performed does not work in hierarchy mode.

The PDF exporting of RadGridView does not work correctly for Arabic text. The exported result revers the Arabic text.

Workaround:

List<object> list = new List<object>(array);
this.radGridView1.DataSource = list;

You cannot changed the value of a check box cell for more than one child rows in object relation hierarchy.

In html view definition and hierarchy mode, the RadGridView throws exception when the TableElement is in explorer bar mode.

You cannot select cells from first and last column when the RadGridView is in right to left mode.

Horizontal cell navigation causes sometime scrolling per page instead of paging to the next invisible column.

Exception is thrown if the data source of second template is changed and rows are expanded in hierarchy.

The GetLookUpValue method of GridViewComboBoxColumn throws exception when the column shows enum values.

If you show a hidden form that hosts a RadGridView control instance, the filtering does not perform correctly.

The maximum vertical scroll position is not accurate when the new row is on the bottom, sorting is applied and new row is added.

The CellClick event is fired when the mouse button is released after scrolling.

When you set the value of unbound column in bound mode of RadGridView, the cell is not updated.

The ConditionalFormatingObjectList of RadGridView's columns cannot be modified at design-time.

The ValueChanged event of RadGridView is fired when the RadDateTimeEdior has null value and the popup is opened.

The GridSpinEditor of RadGridView changes its value automatically to its maximum.