I set up posts with images at around midnight each night. The images are updated from a flickr photoset I set up for that day, and are uploaded automatically from my computer when I add images to a certain folder.
So every night a bit after midnight I set up a new post for the day's images, and make it sticky. Of course I'm going to be doing the same thing the next night, so I want it to unstick at midnight so the next sticky post can be put up. I'd set the unstick day to the next day (let's say I'm setting up a post and it's July 1 at 12:13am, I'd then set up the post, make it sticky, click OK, and set the unstick time to July 2 at 00:00, then publish/update the post).
Sometimes I'd check my blog to see if things were going well, and I'd notice that my sticky images post wasn't at the top of the blog anymore. I'd edit the post and check to see what's going on, and the post was now not sticky and the unstick time was unset.
Now if I do this manually, without the plugin installed, my posts stay sticky and I have to manually unstick them when I set up the new images post for the day.
If you need other info, let me know. I hope you can fix it.