5.x-1.6 contained a stupid last-minute, not-enough-testing mistake which even opened security holes if you allow users to specify the alt attribute of an image in a node. See SA-2008-008 - Meta tags - Arbitrary code execution for the advisory.
Official stable release compatible with Update status version 5.x-2.0. Only a few minor bugs have been fixed since the 5.x-1.0-beta release:
Release candidate; see CHANGELOG.txt for more information.
This update contains the bugfixes mentioned by agilpwc. No other changes from version 1.5 have been made at this time.
This release cleans up packaging errors.
Various small fixes