It seems that the pg_lowrite function was using strlen() to calculate the amount of data to write. This meant that it would not write data correctly if there was a null byte in it. This can be fixed by the following patch which changes it to use the str->value.str.len variable for the amount of data to write.

*** pgsql.c.orig        Mon Jun 29 13:36:54 1998
--- pgsql.c     Wed Jul 22 10:28:10 1998
***************
*** 1311,1316 ****
--- 1311,1317 ----
                        id = pgsql_id->value.lval;
                        convert_to_string(str);
                        buf = str->value.str.val;
+                       buf_len = str->value.str.len;
                        break;
                default:
                        WRONG_PARAM_COUNT;
***************
*** 1323,1329 ****
                RETURN_FALSE;
        }
  
-       buf_len = strlen(buf);
        if ((nbytes = lo_write((PGconn *)pgsql->conn, pgsql->lofd, buf, buf_len))==-1) {
                RETURN_FALSE;
        }
--- 1324,1329 ----