Reason for Decline: this is desired behavior and this is how the docking control in Visual Studio work as well. If one needs to implement such behavior this can be achieved using the events of the Form (floating window):

  void radDock1_FloatingWindowCreated(object sender, FloatingWindowEventArgs e)
        {
            if (radDock1.ActiveWindow.Text == "ToolWindow1")
            {
                e.Window.FormElement.TitleBar.DoubleClick -= TitleBar_DoubleClick;
                e.Window.FormElement.TitleBar.DoubleClick += TitleBar_DoubleClick;

                e.Window.FormElement.TitleBar.MaximizeButton.Click -= MaximizeButton_Click;
                e.Window.FormElement.TitleBar.MaximizeButton.Click += MaximizeButton_Click;
            }
        }

        void MaximizeButton_Click(object sender, EventArgs e)
        {
            if (toolWindow1.Tag == "DoubleClicked")
            {
                RadElement btn = (RadImageButtonElement)sender;
                Form form = (Form)btn.ElementTree.Control;
                form.Location = new System.Drawing.Point(10000, 10000);

                RedockService service = this.radDock1.GetService<RedockService>();
                service.RestoreState(toolWindow1, DockState.Docked, true);
            }
            toolWindow1.Tag = null;
        }

        void TitleBar_DoubleClick(object sender, EventArgs e)
        {
            toolWindow1.Tag = "DoubleClicked";
        }