This has really been happening ever sense 1.3, what would happen is that I would leave my world to take a break or quit for the day and when I'd come back my world would have a rollback. my builds would be gone and stuff would disappear. I made sure I pressed save and quit but my stuff still disappears. I tryed to delete my lancher and redownload it but that did't work. so I tryed to see what all changed from 1.2 to 1.3 and I noticed something. in 1.3 and all it later updates there was no more auto save when pauseing. I downgradeed to 1.1 again and stared a new world and there was no more rollbacks. so the lack of the auto save must be the problem.