The expected behavior should be similar to Visual Studio, once a maximized floating window starts being dragged it should go to a normal state so that the window under it is visible.

How to reproduce: just maximize a floating window, then start dragging it from the title bar, the docking guides will appear which do not help much since the window is still maximized.

Workaround: handle the Starting event of the DragDropService and change the WindowState of the window
public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
        
        DragDropService service = this.radDock1.GetService<DragDropService>();
        service.Starting += Service_Starting;
    }

    private void Service_Starting(object sender, StateServiceStartingEventArgs e)
    {
        FloatingWindow fw = e.Context as FloatingWindow;
        if (fw != null && fw.WindowState == FormWindowState.Maximized)
        {
            fw.WindowState = FormWindowState.Normal;
            fw.Location = new Point(Cursor.Position.X - fw.Size.Width / 2, Cursor.Position.Y);
        }
    }
}