That happened to me while I was looking through worlds for houses to save to the library and add to a CAW town. Since I wasn't opening the worlds to play, I returned to the main menu each time I finished in one world. Every single world I opened after closing the first one had all of the town's ghosts placed in houses as residents. I didn't know at first that they were all ghosts, but I saved the households from the first time it happened, and placed them in my build & edit town. Then once I knew their names, I looked up the world where I had found them on the wiki, and sure enough, they were all the ghosts from that town.
