I've recently started to work with AVCHD 3D/Progressive - H264 MVC material and even though kdenlive works fine with it, it treats it as 2D, so I guess it is only using the left view of the video.
I suppose 3D support or the ability to "split" the left and right view into separate clips (making it easy to i.e. create anaglyph 3D videos) is up to ffmpeg/libavcodec, and as far as I could find out, support for decoding H264 MVC has been discussed but not yet started.
There is at least one (commercial, non-OpenSource) tool, 3dtv.at MVC to AVI Converter, available which works fine but only runs on Windows. The Intel Media SDK 2013 contains sample code allowing to decode H264 MVC into one YUV video per view, but I could not get it to work.
Any other experiences with such material and kdenlive?
I'd be happy to assist/contribute where I can, in testing and providing sample videos, unfortunately I only know how to write code in Java.