I did some basic google'ing and didn't find this...so help is appreciated. I am running 10.9. When I highlight a group of photos and open them with Cmd-O, sometimes Preview.app opens them in multiple instances or "groups" of Preview.app I haven't been able to determine what causes this, how to prevent it, or what determines which images are grouped in one instance of preview versus another. Thanks for your time! ---------- It was tucked in the obvious Preview preferences... Any idea how it determines "groups"? all the files I am attempting to open have similar creation times.