I generated a 1920x1080p @ 25fps HD clip according to these instructions:
http://www.kdenlive.org/forum/rendering-1920-becomes-1440-yet-still-play...
I can play it OK in Movie Player on Ubuntu 10.04, but it says the duration is only 5'19" instead of what it actually is. FFMpeg reports the duration as 00:24:33:00, which is correct. When it gets to the end of the slider at 5-1/2 minutes, it continues to play.
But when I import it back into kdenlive, it says the duration is only 19 seconds! What does ffmpeg do differently than kdenlive? I thought that it used ffmpeg internally for a lot of things.

"M2T's are HDV? mpeg2 1440x1080? rather than 1920x1080, non square pixels and all that, as per your 1440 link?"
No, I meant this post from Dan Dennedy further down in that thread:
http://www.kdenlive.org/forum/rendering-1920-becomes-1440-yet-still-play...
I followed those instructions.