I am struggling with the following issue. I want to convert an MP3 ADTS into pure a MP3. I am using AVConv on Ubuntu 12.10. The outcome is a file that has the same size, but the duration is now longer.

$ ls -l
total 6436
-rw-r--r-- 1 teuf teuf 6586514 nov.  25 09:25 Blindsided_Bon_Iver.mpga

$ file Blindsided_Bon_Iver.mpga 
Blindsided_Bon_Iver.mpga: MPEG ADTS, layer III, v1, 160 kbps, 44.1 kHz, JntStereo

$ avconv -i Blindsided_Bon_Iver.mpga -c copy Blindsided_Bon_Iver.mp3
avconv version 0.8.4-4:0.8.4-0ubuntu0.12.04.1, Copyright (c) 2000-2012 the Libav developers
  built on Nov  6 2012 16:50:25 with gcc 4.6.3
[mp3 @ 0x8c6e240] max_analyze_duration reached
Input #0, mp3, from 'Blindsided_Bon_Iver.mpga':
  Duration: 00:05:29.29, start: 0.000000, bitrate: 160 kb/s
    Stream #0.0: Audio: mp3, 44100 Hz, stereo, s16, 160 kb/s
Output #0, mp3, to 'Blindsided_Bon_Iver.mp3':
  Metadata:
    TSSE            : Lavf53.21.0
    Stream #0.0: Audio: libmp3lame, 44100 Hz, stereo, 160 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (copy)
Press ctrl-c to stop encoding
size=    6432kB time=329.30 bitrate= 160.0kbits/s    
video:0kB audio:6432kB global headers:0kB muxing overhead 0.002080%

$ ls -l
total 12868
-rw-rw-r-- 1 teuf teuf 6586129 nov.  27 22:26 Blindsided_Bon_Iver.mp3
-rw-r--r-- 1 teuf teuf 6586514 nov.  25 09:25 Blindsided_Bon_Iver.mpga

$ file Blindsided_Bon_Iver.mp3
Blindsided_Bon_Iver.mp3: Audio file with ID3 version 2.4.0, contains: MPEG ADTS, layer III, v1,  32 kbps, 44.1 kHz, Stereo

Amarok shows the new file has a duration of 25:27 and has a lot of silence.

Am I using an incorrect option? Is it a bug in AVConv? Any ideas how to fix it?