Glib GString: memory not freed ?

[Matt <matt flandrescartouches com>]

Hello,

I am new to glib ;-) 

I use mtrace() to find memory leaks in my code and I found something strange 
with GStrings : some memory is maybe not freed.

Try the following example:

#include <glib.h>
#include <stdio.h>
#include <mcheck.h>

int main()
{
        GString *gstring;
        mtrace();

        gstring = g_string_new(NULL);

        printf("Hello, World!\n");

        g_string_sprintf(gstring, ", %s!","World");
        printf("Goodbye%s\n",gstring->str);

        g_string_free(gstring,TRUE);

        muntrace();
        return 0;
}

matt:matt$ ./gstring && mtrace ./gstring $MALLOC_TRACE
Hello, World!
Goodbye, World!

Memory not freed:
-----------------
   Address     Size     Caller
0x08051668     0x34  at /tmp/glib-1.2.10/gmem.c:178
0x080516a0      0x8  at /tmp/glib-1.2.10/gmem.c:178
0x080516b0    0x400  at /tmp/glib-1.2.10/gmem.c:178
0x08051ab8     0x34  at /tmp/glib-1.2.10/gmem.c:178
0x08051af0    0x400  at /tmp/glib-1.2.10/gmem.c:178

Looking into the code of gstring.c, I found:
G_LOCK_DEFINE_STATIC (string_mem_chunk);
static GMemChunk *string_mem_chunk = NULL;

Is that data really freed with a g_string_free(gstring,TRUE); ?
Where is my mistake ?

Regards,
Matt