Flash export from widescreen video (DV PAL Widescreen) is incorrect - the image is still anamorph even though the format (or mplayer which I used for testing) does not store requested aspect ratio. I think other exports may have the same problem too.
I would make my own render settings, but I was unable to find any information how to rescale during render (see also my forum post http://www.kdenlive.org/bbforum/viewtopic.php?f=11&t=187).
I am using Kdenlive from SVN:
FFmpeg SVN version:
Last Changed Date: 2007-08-12 17:47:27 +0200 (Sun, 12 Aug 2007)
MLT SVN version:
Last Changed Date: 2007-08-04 09:43:36 +0200 (Sat, 04 Aug 2007)
MLT++ SVN version:
Last Changed Date: 2007-06-12 08:00:29 +0200 (Tue, 12 Jun 2007)
Kdenlive SVN version:
Last Changed Date: 2007-08-12 15:40:09 +0200 (Sun, 12 Aug 2007)