Issue with "Save As" for a top-level assy forcing upgrades to SW2016 for any parts and subassys that were last saved using an older version of Solidworks?

Is there any way of stopping this? I often create new assys by "Save as Copy" of a similar assy and then making minor changes to the parts underneath.  When I "Save" an assy, it does not try and force an upgrade to SW2016 for those parts/subassys saved in older versions of SW.  Thanks.