jerking rendering output

Hello all,

my current project deals with ntsc video clips and I think I've discovered
a rendering bug.

The situation:

My camera produces video clips in a resolution of 640x480 with 29.97 fps.
I convert this clips to mpeg2 for further editing. During the conversion I keep
the resolution and framerate. The converted clips run smooth in Mplayer or avidemux.

I import the clips into kdenlive (0.6 from svn), cut it and apply some transitons.

The observation:

At the timeline the frame counter counts from 0 to 28 within a second.

My expectations would be a counting from 0 to 29 and sometimes (to stay in sync) to 28 within a second.
So we get an overall frame rate of 29.97 frames/sec. (My assumption is we have 29 frames per second
instead of 29.97 frames per second.)

If the video is finished I export it to a file.

In the kdenlive preview window the movie runs really smooth and without any jerks but
the rendered video now is a litte bit jerky (no matter what format I use).

If I load this rendered Video into avidemux I can see every 10th frame
is a litle jump.
It seems the 29 frames of every second (see my note to the frame counter)
are distributed over the 29.97 frames during the rendering process in ffmpeg.

That destroys the smoothness of any movement in the video.

Can I avoid this effect by using other parameters for the rendering command?

Thanks for reading and any help would be appreciated!

Best regards