I had this happen a few times a couple weeks ago, I thought I was going crazy.  I figured I must not have been saving on exit.....which if it was one file, I would have bought that, but it happened on multiple files over the course of a couple days.

Haven't noticed it lately though.   Maybe try doing a REFRESH updates (not a regular update, its at the bottom of the updates list), maybe an update didnt install completely or correctly?