How to reproduce: see the attached video

Workaround:
public partial class Form2 : Form
{
    public Form2()
    {
        InitializeComponent();

        this.radPivotFieldList1.DragDropService = new CustomPivotFieldListDragDropService(this.radPivotFieldList1);
    }

    private void Form2_Load(object sender, EventArgs e)
    {
        // TODO: This line of code loads data into the 'nwindDataSet.Orders' table. You can move, or remove it, as needed.
        this.ordersTableAdapter.Fill(this.nwindDataSet.Orders);

    }
}

public class CustomPivotFieldListDragDropService : PivotFieldListDragDropService
{
    private RadPivotFieldList fieldList;
    private Telerik.WinControls.UI.PivotFieldList.FieldPayload payload;

    public CustomPivotFieldListDragDropService(RadPivotFieldList fieldList)
        : base(fieldList)
    {
        this.fieldList = fieldList;
    }

    protected override void PerformStart()
    {
        base.PerformStart();

        Telerik.WinControls.UI.PivotFieldList.IField draggedField = this.GetField(this.Context);

        if (draggedField == null)
        {
            this.Stop(false);
            return;
        }

        this.payload = new Telerik.WinControls.UI.PivotFieldList.FieldPayload(draggedField);
    }

    protected override void OnPreviewDragOver(RadDragOverEventArgs e)
    {
        RadElement targetElement = this.DropTarget as RadElement;
        Telerik.WinControls.UI.PivotFieldList.IField targetField = this.GetField(targetElement);

        if (targetElement != null && targetElement.ElementTree.Control == this.fieldList.ReportFiltersControl && this.payload != null)
        {
            foreach (Telerik.WinControls.UI.PivotFieldList.IField field in this.fieldList.ViewModel.Filters)
            {
                if (field.FieldInfo == payload.DraggedField.FieldInfo &&  this.Context is TreeNodeElement ))
                {
                    e.CanDrop = false;
                    this.payload.SetDestination(null);
                    this.payload.RemoveFromSource = false;

                    return;
                }
            }
        }

        base.OnPreviewDragOver(e);
    }

    private Telerik.WinControls.UI.PivotFieldList.IField GetField(object context)
    {
        RadListVisualItem listItem = context as RadListVisualItem;
        TreeNodeElement treeItem = context as TreeNodeElement;
        PivotFieldListItemButton button = context as PivotFieldListItemButton;

        if (button != null)
        {
            listItem = button.Owner;
        }

        Telerik.WinControls.UI.PivotFieldList.IField field1 = null, field2 = null;
        if (listItem != null && listItem.Data != null)
        {
            field1 = listItem.Data.DataBoundItem as Telerik.WinControls.UI.PivotFieldList.IField;
        }

        if (treeItem != null && treeItem.Data != null)
        {
            field2 = treeItem.Data.DataBoundItem as Telerik.WinControls.UI.PivotFieldList.IField;
        }

        return field1 ?? field2;
    }
}