Propel 1.5.6 was just released. It is yet another (almost) monthly bugfix release, closing about a dozen issues. You can find the full changelog in the Propel 1.5 documentation.
To upgrade, use your favorite distribution:
> svn checkout http://svn.propelorm.org/tags/1.5.6
> sudo pear upgrade propel/propel-generator > sudo pear upgrade propel/propel-runtime
Found a typo ? Something is wrong in this documentation ? Just fork and edit it !