Desktop spaces keep re-arranging despite all options being set to leave them alone.

We're using El Capitan, the latest version this 2008 MacBook Pro can run. Every so often, and more often lately, the Spaces on the desktop are re-arranged. All the options to control this are set to leave them alone and don't move them. But despite the settings in Mission Control and Finder/View they are moved anyway. And when they move, the arrangement is random. Can it be fixed?