I use the Preview.app to review and compare jpg files, and it's not unusual for me to have in excess of 100 open at a time. After I upgraded to Mountain Lion, I noticed that Preview.app will open somewhere in the neighborhood of 50 files in their own window, but then it begins to open any additional files within an already open window. I've discovered that I can select the second file in the side bar, right click and choose "open in new window", but it's a time-consuming hassle.
I've checked the preferences, and "Open each file in it's own window" is selected, so I'm not sure what's going on. Has anyone else experienced this, and is there a way to fix it? It's incredibly annoying.
As you can see in the screenshot a number of files will open in their own window, then at a certain point additional files all begin opening in one window (as seen in the file on the lower right). As I said above, I can right click on a thumbnail in the sidebar and make the image open in it's own window, but why it suddenly makes the switch arbitrarily is beyond me. The previous version I was working with (OS 10.6.8) didn't have this issue.