I added some audio streames in video editing mode and by animating (ALT-A) there is just one channel (left in my case), where the other is silent. Same blend file in 2.61 works with stereo
Assume you're using you're using OpenAL library which is unfortunately broken in release. I hope updated archives will be uploaded to blender.org soon, but meanwhile you might want to try this thing: download .dll files from https://svn.blender.org/svnroot/bf-blender/trunk/lib/win64/openal/lib/ and replace .dll placed near your blender.exe. This should repair OpenAL output.
Another thing you might do meanwhile is to switch to SDL backend.
Thanks for the report, but in fact is was already fixed in current svn, just platform maintainer should update archives. So closing it.