issue with lo_lseek - it returns 4

Hi,
I'm trying to get lo size via libpq before starting reading it (postgres server 8.3.5). lo_lseek always returns 4 (actual size is > 1M).
I query table with "select photo from employee where id='xxxx'". It returns lo oid integer as expected. Then I use following code to obtain size of the lo object:
    int lobj_fd = lo_open(conn, lobjId, INV_READ);  // returns valid fd, ok

    lo_lseek(conn, lobj_fd, 0L, SEEK_END );
    size = lo_tell(conn, lobj_fd);   // always returns 4, error?

Is it possible to obtain lo object size before reading it?

Thank you
Konstantin