For reference, on July 2 we upgraded the version of eXist bundled with Orbeon Forms. We used to be on 1.2.4 and are now on 1.2.6. You will get this new version of eXist if you download a nightly build created after July 2 (and it will obviously come in upcoming releases as well).
eXist 1.2.5 and 1.2.6 are maintenance releases; they don't add new features and only fix issues. You can find the release notes for those versions on the eXist blog at:
http://atomic.exist-db.org/blogs/eXist/eXist125http://atomic.exist-db.org/blogs/eXist/eXist126Alex