First, I'm not sure how it got updated to begin with ... is it automatic? I show a database backup on 9/24 but I was on vacation at the time (my PC would have been turned on though).

Upon returning and noticing C5 was updated, I also noticed the posts on my blog are messed up. I've got 7 posts and 4 of them are duplicated.

I don't know how or why this happened. I looked for previous versions and they're not right either so I can't go back to the original. The dates from the past versions are correct so it doesn't look like they've been overwritten after they'd originally been posted so I'm very confused. (e.g., this last post was from 9/12 but the others were all posted before that and none of them have versions dated after their post date).

Next steps: I tried restoring and ended up with a fatal error, I was able to fix that with the help of this post:
http://www.concrete5.org/community/forums/chat/lost-my-website./...

I messed around a bit and went back to an older version of C5, updated a post back to what it should have been, then upgraded to the new version again and that post completely disappeared!

Next, I restored to a backup I'd done last night. I got the "dissapeared" post back, but it's still the wrong one.

I guess I'm going to go in and revise each of the duplicates, but I'm not understanding why this happened and how to avoid it in the future.