I've got running copies of both preview and keynote open right now with no active or open documents in either. I think what you're seeing is not a closing-wind

I've got running copies of both preview and keynote open right now with no active or open documents in either. I think what you're seeing is not a closing-windows behavior but a memory-saving one. MacOS can and will close or suspend applications that are not actively doing anything to free up memory and CPU cycles. This is enabled by 2 features/APIs Automatic and Sudden Termination. See http://arstechnica.com/apple/2011/07/mac-os-x-10-7/8/ http://arstechnica.com/apple/2011/07/mac-os-x-10-7/8/ for the Full Siracusa. For obvious reasons, applications that properly tell the OS they are in such a state are the ones you'll most often see this behavior in, and Apple's first-party applications are written that way.