I'm preparing to teach an iText class in Paris, and to give some demo's in Oakland. I'm currently making a new set of examples for some new chapters I'm going to write (maybe a third book, not a revision of the second edition, but a book with some advanced topics). Whilst making examples to explain the different options available in XML Worker, I found some bugs and I also thought about some functionality that was missing.
It would be a pity if I demonstrated my new examples in the next few weeks without having a new release with the latest changes, so that's why I made iText 5.2.1 one month after iText 5.2.0 was published. For more info about the release, please check the changelog.