With the 'keep ratio' box checked, the picture aspect ratio is not maintained while adjusting the picture size by dragging the picture border (edge or corner with little green squares). I just discovered that the aspect ratio is maintained while adjusting size inside the picture dialog box. 'keep ratio' should also apply while dragging image size.
User Error! @kevinp54321@gmail.com this checkbox indeed is only for automatic calculation of the 2nd value for size in the dialog. If you want to keep ratio for mouse operations press <shift> when dragging control points.
*** This bug has been marked as a duplicate of bug 84565 ***