mp3 invalid new backstep 
with audible glitch

observed with mp3 files
from and upwards (of these bitrates):
8kHz     64k

sample provided 8kHz at 64k 
produces a deafening glitch
(encoded with lame 3.97)

ffmpeg -i 8.64.mp3 out8.wav
FFmpeg version SVN-r14231, Copyright (c) 2000-2008 Fabrice Bellard, et al.
  configuration: --enable-memalign-hack --enable-postproc --enable-swscale --ena
ble-gpl --enable-liba52 --enable-libfaac --enable-libfaad --enable-libgsm --enab
le-libmp3lame --enable-libnut --enable-libvorbis --enable-libtheora --enable-lib
xvid --enable-libx264 --disable-ffserver --disable-ffplay --enable-avisynth --en
able-small --enable-pthreads --extra-ldflags=-static --extra-cflags=-mtune=penti
um4 -mfpmath=sse -msse -fno-strict-aliasing
  libavutil version: 49.7.0
  libavcodec version: 51.60.0
  libavformat version: 52.17.0
  libavdevice version: 52.0.0
  built on Jul 15 2008 04:17:40, gcc: 4.3.1
invalid new backstep 555
Input #0, mp3, from '8.64.mp3':
  Duration: 00:00:07.48, start: 0.000000, bitrate: 69 kb/s
    Stream #0.0: Audio: mp3, 8000 Hz, stereo, 64 kb/s
Output #0, wav, to 'out8.wav':
    Stream #0.0: Audio: pcm_s16le, 8000 Hz, stereo, 256 kb/s
Stream mapping:
  Stream #0.0 -> #0.0
Press [q] to stop encoding
invalid new backstep 555
size=     236kB time=7.56 bitrate= 256.0kbits/s
video:0kB audio:236kB global headers:0kB muxing overhead 0.018188%


ty
tripp