I think I might have messed up some setting. The latest example was when attempting to subdivide an extruded rectangle. The first subdivision went okay.
Selection of the first edge for subdivision
Vertex selection after subdivision
Vertex selection after subdivision of second edge
As soon as I attempted to move this vertex, the first went flying
At this point any attempt at moving either vertex resulted in a type of mirrored movement of the unselected vertex. Even crazier examples happen when certain objects are moved. I have reloaded Blender.app, tried backups and was unsuccessful in finding the cause. Thanks, TOM