ffmpeg can't copy h264 video in mkv

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if i want to change audio format in mkv+h264 video with ffmpeg, i get error. example command line and output:

ffmpeg -i sample.mkv -vcodec copy -acodec libfaac out.mkv
FFmpeg version SVN-r16495, Copyright (c) 2000-2009 Fabrice Bellard, et al.
configuration: --prefix=/buildas --enable-memalign-hack --enable-gpl --enable-nonfree
--enable-postproc --enable-swscale --enable-pthreads --enable-avisynth --enable-libfaac
libavutil 49.12. 0 / 49.12. 0
libavcodec 52.10. 0 / 52.10. 0
libavformat 52.23. 1 / 52.23. 1
libavdevice 52. 1. 0 / 52. 1. 0
libswscale 0. 6. 1 / 0. 6. 1
libpostproc 51. 2. 0 / 51. 2. 0
built on Jan 8 2009 15:33:21, gcc: 4.3.2
Input #0, matroska, from 'sample.mkv':
Duration: 00:01:17.53, start: 0.000000, bitrate: N/A
Stream #0.0: Video: h264, yuv420p, 688x384, 23.98 tb(r)
Stream #0.1: Audio: vorbis, 48000 Hz, 5.1, s16
Output #0, matroska, to 'out.mkv':
Stream #0.0: Video: 0x0000, yuv420p, 688x384 [PAR 1:1 DAR 43:24], q=2-31, 23.98 tb(c)
Stream #0.1: Audio: libfaac, 48000 Hz, 5.1, s16, 64 kb/s
Stream mapping:
Stream #0.0 -> #0.0
Stream #0.1 -> #0.1
Press [q] to stop encoding
[NULL @ 0x3ecbd0]error, non monotone timestamps 83 >= 42
av_interleaved_write_frame(): Error while opening file

but if i change -vcodec copy to something like -vcodec huffyuv there is no errors.

Am i doing something wrong?