It's reproducible on Ubuntu 12.04: Import a DV file into Pitivi, and render it as a DVD VOB file. Here's what I get:

maciej@quince:~$ avconv -i src/slideshow/Stand\ By\ Me.vob 
avconv version 0.8.3-4:0.8.3-0ubuntu0.12.04.1, Copyright (c) 2000-2012 the Libav developers
  built on Jun 12 2012 16:52:09 with gcc 4.6.3
[mpeg @ 0x25c89a0] max_analyze_duration reached
[NULL @ 0x25caaa0] start time is not set in estimate_timings_from_pts
Input #0, mpeg, from 'src/slideshow/Stand By Me.vob':
  Duration: 00:03:28.80, start: 1.000000, bitrate: 5242 kb/s
    Stream #0.0[0x1e0]: Video: mpeg2video (Main), yuv420p, 720x576 [PAR 16:15 DAR 4:3], 104857 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc
    Stream #0.1[0x80]: Audio: ac3, 44100 Hz, stereo, s16, 128 kb/s
At least one output file must be specified
maciej@quince:~$ ls -l !$
ls -l src/slideshow/Stand\ By\ Me.vob
-rw-rw-r-- 1 maciej maciej 136822784 Jul 21 23:28 src/slideshow/Stand By Me.vob
maciej@quince:~$ echo "136822784 * 8 / ( 60 * 3 + 28 )" | bc
5262414

The reported total bitrate seems right (5242 kb/s) but the video stream bitrate is set to a wrong value, and doesn't match the actual bitrate of the file which can be estimated by the file size and the media running time.

I talked to guys at #pitivi and I was redirected here as the issue is potentially a problem in gst-ffmpeg.

The problem seems to be bound with the video stream, and not the container.

I can do e.g. this:
avconv -i src/slideshow/Stand\ By\ Me.vob -acodec copy -vcodec copy foo.mp4

,,,and:

maciej@quince:~$ avconv -i foo.mp4 
avconv version 0.8.3-4:0.8.3-0ubuntu0.12.04.1, Copyright (c) 2000-2012 the Libav developers
  built on Jun 12 2012 16:52:09 with gcc 4.6.3
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'foo.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2mp41
    encoder         : Lavf53.21.0
  Duration: 00:03:28.96, start: 0.000000, bitrate: 5137 kb/s
    Stream #0.0(und): Video: mpeg2video (Main), yuv420p, 720x576 [PAR 16:15 DAR 4:3], 104857 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc
    Stream #0.1(und): Audio: ac3, 44100 Hz, stereo, s16, 128 kb/s
At least one output file must be specified

Still "104857 kb/s", and the problem seems to travel with the video data.

The problem is reproducible so I should be able get more information if necessary.