As of the DK v.8, visible extent and layer activity information is automatically stored to the project file upon SaveAll / SaveProjectxxx call. VisibleExtent is reapplied after call GIS.Open method.
Do not call GIS.FullExtent. If you call GIS.Open to open a single layer, then FullExtent will be called internally.
GIS.Open( 'myproject.ttkgp' )
// GIS.FullExtent ; <--- THIS IS OBSOLATE