I captured the output of the same 30 seconds of audio from Noatun/arts/mpeglib and also from mpg321/libmad, then encoded them with FLAC. Available here:
http://www.marm.org.uk/mpeglib-decode-bug-mad-output.flac http://www.marm.org.uk/mpeglib-decode-bug-mpeglib-output.flac -- marm