People familiar with the matter say the new pre-release distribution, labeled Mac OS X 10.5.3 build 9D22, adds 15 new bug fixes to a laundry list now spanning over 170 items long.
Among the latest improvements is a fix for an issues that prevented some Mac systems from properly rejoining an AirPort wireless network after awaking from sleep.
Meanwhile, other corrections rectify delayed shutdown problems, clipping during CD or DVD sharing, and crashes while enabling System Mode.
Apple is believed to have already fixed two of its more publicized issues, including a Wi-Fi connection problem preventing the use of new MacBooks on New York state schools' wireless networks and graphics anomalies on Intel Penryn-based portable systems.
Documentation reported to have accompanied build 9D22 suggests that development of the Leopard update is rapidly winding down. Apple is said to have asked developers to focus their testing efforts on 12 core system components, down from 17 in the previous build, and 24 in the build before that.
This includes Active Directory, Back To My Mac, Mail, Spaces, and several more of the most essential underpinnings of the OS, according to those familiar with the update.
Sources speaking privately to AppleInsider in recent days have said Apple hopes to release Mac OS X 10.5.3 within the next two to three weeks.