_csi_intern_string:

    if (istring == NULL) {
        istring = _csi_perm_alloc (ctx,
                                   sizeof (csi_intern_string_t) + len + 1);


_csi_perm_alloc is where the fun happens! (cleaned up a bit)
    csi_chunk_t *chunk = _csi_alloc (ctx, sizeof (csi_chunk_t) + chunk_size);
    chunk->ptr = (char *) (chunk + 1);
    ptr = chunk->ptr;
    return ptr;

in _csi_intern_string , if _csi_hash_table_insert fails:
    _csi_free (ctx, istring);

so basically it does malloc(something) and free(something + sizeof(csi_chunk_t)).