I have an issue with the latest version of Organize Series (2.4.3) and WordPress 3.5.
Everytime I add a new post to one of my article series the number of the post in the series changes. If I have 15 posts in my series and add a new post (or schedule one) the other posts are set to -1, eg. post 15 becomes 14, 14 becomes 13 and so forth.
It might also occur when I edit a post earlier in the series.