The attached videos demonstrate the present behavior and the desired one

How to reproduce:
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();

        this.radDock1.EnableFloatingWindowSnapping = true;
        DragDropService svc = this.radDock1.GetService<DragDropService>();
        svc.DragDropMode = DragDropMode.Preview;
    }
}