RadVirtualGrid retains pending off-screen PushCellValue values across Reset(), Reset(rowCount, columnCount), and DataProvider replacement. When indices are reused for different data, the first realized cell consumes the stale value instead of retrieving the value from the new DataProvider. A pushed null renders a blank. Scrolling away and back retrieves the correct value. This can display data from a different item once after a dataset change.

The FilterColumn method does not position the filtering popup on the passed column index when it is opened.

A workaround to this behavior would be to manually position the filtering popup using the following approach:

this.virtualGrid.FilterColumn(2);

var virtualizingCanvasBase = this.virtualGrid.ChildrenOfType<VirtualizingCanvasBase>().FirstOrDefault();

var columnsRenderInfoInfo = virtualizingCanvasBase.GetType().GetProperty("ColumnsRenderInfo", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);

var columnsRenderInfo = columnsRenderInfoInfo.GetValue(virtualizingCanvasBase);

var offsetMethodInfo = columnsRenderInfo.GetType().GetMethod("OffsetFromIndex");

var filteringPopupPropertyInfo = this.virtualGrid.GetType().GetProperty("FilteringPopup", System.Reflection.BindingFlags.Instance | System.Reflection.BindingFlags.NonPublic);

Popup filteringPopup = (Popup)filteringPopupPropertyInfo.GetValue(this.virtualGrid);

filteringPopup.HorizontalOffset = (double)offsetMethodInfo.Invoke(columnsRenderInfo, new object[1] { 2 });

The FilterColumn method should be called, in order for the filtering Popup to be created.

HeaderSizeNeeded is fired twice with the same index and affects the header row width. 

The CellDecorationsNeeded event isn't raised for pinned columns/rows

I would expect this event would be raised regardless of pinned state. Otherwise the UI would not be consistent when columns/rows are pinned.

// SomeVirtualGrid.xaml.cs
public SomeVirtualGrid()
{
    InitializeComponent();
    vg.PinColumnLeft(0);
    vg.PinColumnLeft(1);
    vg.PinColumnLeft(2);
}