Ableton Live 8.1.4 is now available. They list improvements as:
“Combination Mode is now active when multiple Akai APC40/20s are in use. This means that the topmost controller selected in your preferences will control tracks 1-8, the second controller selected will control tracks 9-16, and so on. When an APC40 and an APC20 are connected at the same time, the APC20's buttons will default to Track Selection, and its faders will default to volume.”
For list of bugfixes checkout the forum post - http://forum.ableton.com/viewtopic.php?f=1&t=141021
You can update to the latest version here - http://www.ableton.com/latest_versions
It's good policy not to upgrade mid-project. Since I’m in final mix down on my album with 8.1.3 and all is well so I won’t upgrade for a week or two. So, if you upgrade, drop a comment on this post and let us all know how it’s going.