[mencoder] No audio in last few seconds after encoding?

[MacDada]

Hi!

I use Mencoder to add watermark and subtitles to my site's videos. The problem is that sometimes, after encoding, a video doesn't have any sound in the last few seconds.

Example file before:
http://filmixxy.pl/uploads/problematic_video_before.m4v

Example file after:
http://filmixxy.pl/uploads/problematic_video_after.mp4

My encoding script:

#!/bin/bash

# loading params:
FILMIXX_ID=$1
MOVIE_FILE_PATH=$2
OUTPUT_MOVIE_FILE_PATH=$3
SUBTITLES_FILE_PATH=$4
LOGO_VERTICAL_POSITION=$5

LOGO_FILE_PATH="XXXXXXXX/watermark.rgba"
LOGO_FIFO_FILE_PATH="XXXXXXXXXX/watermark.fifo"

# deleting old files if necessary:
rm $LOGO_FIFO_FILE_PATH
rm $OUTPUT_MOVIE_FILE_PATH

# creating fifo to encode watermark:
mkfifo $LOGO_FIFO_FILE_PATH

# pasting watermark to fifo:
(echo "RGBA32 129 20 $LOGO_VERTICAL_POSITION 5 0 1"; cat $LOGO_FILE_PATH) > $LOGO_FIFO_FILE_PATH  &

# encoding video:
/usr/bin/mencoder $MOVIE_FILE_PATH \
-o $OUTPUT_MOVIE_FILE_PATH \
-fontconfig -font 'Arial:style=Bold' \
-ffactor 2 \
-sub $SUBTITLES_FILE_PATH -utf8 \
-lavfopts format=mp4 \
-faacopts mpeg=4:object=2:raw:br=64 \
-vf bmovl=0:0:$LOGO_FIFO_FILE_PATH \
-oac faac -mc 0 -noskip \
-ovc x264 -sws 9 \
-x264encopts nocabac:level_idc=30:bframes=0:global_header\
:threads=auto:subq=3:frameref=6:partitions=all:trellis=1:chroma_me:me=umh \
-of lavf

# deleting not usefull anymore fifo file:
rm $LOGO_FIFO_FILE_PATH

exit 0

Any idea what's causing the problem?
Thanks in advance!