Alsa project use MTrace with a lot of memory leak info

Question

When I used MTrace to detect memory leak in ALSA sample project which is at ALSA's official website, it shows a lot of memory leak info.
The sample project's website is Here!
I just add some MTrace code.

#include <alsa/asoundlib.h>
#include <mcheck.h>

static char *device = "default";                        /* playback device */
snd_output_t *output = NULL;
unsigned char buffer[16*1024];                          /* some random data */
int main(void)
{
    mtrace();
    int err;
    unsigned int i;
    snd_pcm_t *handle;
    snd_pcm_sframes_t frames;
    for (i = 0; i < sizeof(buffer); i++)
            buffer[i] = random() & 0xff;
    if ((err = snd_pcm_open(&handle, device, SND_PCM_STREAM_PLAYBACK, 0)) < 0) {
            printf("Playback open error: %s\n", snd_strerror(err));
            exit(EXIT_FAILURE);
    }
    if ((err = snd_pcm_set_params(handle,
                                    SND_PCM_FORMAT_U8,
                                    SND_PCM_ACCESS_RW_INTERLEAVED,
                                    1,
                                    48000,
                                    1,
                                    500000)) < 0) {   /* 0.5sec */
            printf("Playback open error: %s\n", snd_strerror(err));
            exit(EXIT_FAILURE);
    }
    for (i = 0; i < 16; i++) {
            frames = snd_pcm_writei(handle, buffer, sizeof(buffer));
            if (frames < 0)
                    frames = snd_pcm_recover(handle, frames, 0);
            if (frames < 0) {
                    printf("snd_pcm_writei failed: %s\n", snd_strerror(frames));
                    break;
            }
            if (frames > 0 && frames < (long)sizeof(buffer))
                    printf("Short write (expected %li, wrote %li)\n", (long)sizeof(buffer), frames);
    }
    snd_pcm_close(handle);
    return 0;
}

Then use command to compile as blow:

g++ pcm_min.cc -g -lasound -o alsa_test

Execute alsa_test:

$ export MALLOC_TRACE=/tmp/t
$ ./alsa_test
$ mtrace ./alsa_test $MALLOC_TRACE

Then it will show memory leak info like this:

    Memory not freed:
-----------------
           Address     Size     Caller
0x000000000075b450     0x10  at 0x7f8ff4f728e8
0x000000000075b470     0x20  at 0x7f8ff4f72904
0x000000000075b4a0     0x10  at 0x7f8ff5249373
0x000000000075b500     0x20  at 0x7f8ff5257961
0x000000000075b530     0x1a  at 0x7f8ff4c0248a
0x000000000075b560     0x48  at 0x7f8ff4f6c899
0x000000000075b6c0     0x25  at 0x7f8ff524cef4
0x000000000075b6f0      0x6  at 0x7f8ff4f6c9e5
0x000000000075b710     0x48  at 0x7f8ff4f6c899
0x000000000075b760      0x5  at 0x7f8ff4f6c9e5
0x000000000075b780     0x41  at 0x7f8ff524cef4
0x000000000075b7d0     0x28  at 0x7f8ff524cef4
0x000000000075b800     0x20  at 0x7f8ff466b627
.........

It is whose problem? MTrace? ALSA? Why?