In versions prior 18.2, the floating window's position relates to the main window's position (where the DockLayoutManager manager is placed), not relative to the floating window's parent window. This occurs because the Window.GetWindow() method returns the window in which the DockLayoutManager is placed. For example, with this behavior, it is not possible to display a floating window in the center of its parent window: WindowedDocumentUIService defined in a layout panel uses a window where DockLayoutManager is placed as owner.
In v18.2, the Window.GetWindow() method returns an actual window that owns the current floating panel.
This breaking change may affect the code that used the Window.GetWindow() method.
Starting with v18.2.4, you can set the CompatibilitySettings.MakeGetWindowReturnActualFloatPanelWindow property to false to enable the old behavior.