Committing 1PC transactions would be converted to heuristic hazard cases upon recovery, which is in fact incorrect because these will then undergo 2PC commit retry. This has now been fixed: committing 1PC transactions are now simply forgotten upon recovery.
Empty, committing transactions would needlessly generate logging overhead and also generate needless heuristic warnings upon recovery. This has now been fixed. For the original report, see this forum post.
Improved synchronization to avoid race conditions while checking whether or not a connection is taking part in a transaction. Also see this report in the forums.