Oh, that ! I thought you meant they were jumping about all over the screen.
It's part of the GUI standard for the presentation of multiple windows. The options are Cascade (which you describe), Tile Vertical or Tile Horizontal. Cascading leaves just the window title and File menu visible so you can access each open window with a single click.
You can play with the options by right clicking a vacant area of the Taskbar (down there at the bottom). Never did see much use for tiling myself unless you have a ginormous monitor.
Nothing you can do about it
AFAIK, but then I'm no Windows guru.