Strange RETURN NEXT behaviour in Postgres 8.0

Hi All

I have a quite strange problem with RETURN NEXT statement.
I have a big table with 500 millions of rows running on Postgres 8.0.     Table "public.usno"Column |  Type  |
Modifiers
 
--------+--------+-----------ra     | real   | dec    | real   | bmag   | real   | rmag   | real   | ipix   | bigint |
errbox| box    | 
 
Indexes:   "box_ind" rtree (errbox)   "ipix_ind" btree (ipix)   "radec_ind" btree (ra, "dec")

I actually wrote some procedures in PL/SQL using dynamical queries, 
and once I obtained the following error. 
ERROR:  wrong record type supplied in RETURN NEXT
CONTEXT:  PL/pgSQL function "yyy" line 8 at return next

To solve the problem, I used just the following simple PL/SQL functions, and 
a query "select * from yyy()"

CREATE OR REPLACE FUNCTION xxx(refcursor) RETURNS refcursor AS '
DECLARE query varchar;
BEGIN 
query = ''SELECT * FROM usno'';
OPEN $1 FOR EXECUTE query;
RETURN $1;
END;
' LANGUAGE plpgsql;

CREATE OR REPLACE FUNCTION yyy() RETURNS SETOF usno AS '
DECLARE rec record; 
DECLARE cur refcursor;
BEGIN 
cur=xxx(''curs_name'');
LOOP       FETCH cur into rec;       RETURN NEXT rec;       EXIT WHEN NOT FOUND;
END LOOP;
RETURN;
END;
' LANGUAGE plpgsql;

I was quite surprised by this errors, because I have tried the same
functions on rather same (but smaller table) on Postgres 7.4.6 on my laptop
without any problems.

For debugging purposes, I just have created by hand on Postgres 8.0 machine 
the small table "q3c" with just two rows, but same structure as usno table.     Table "public.q3c"Column |  Type  |
Modifiers
 
--------+--------+-----------ra     | real   | dec    | real   | bmag   | real   | rmag   | real   | ipix   | bigint |
errbox| box    | 
 
Indexes:   "box_ind1" rtree (errbox)   "ipix_ind1" btree (ipix)   "radec_ind1" btree (ra, "dec")

And, after replacing "usno"->"q3c" in the xxx() and yyy(), the query 
"select * from yyy()" worked without problems!!! 

So, how can it be, that my PL/SQL functions works fine on one(smaller)
table, but fails on another(bigger) table.

Thanks in advance for any ideas. Sergey
PS
I have tried my code replacing the declaration 
"rec record;"  by "rec TABLE_NAME%ROWTYPE", and it worked for both (big and
small table), but I don't understand, why it doesn't work with the type
"record".

------------------------------------------------------------
Sergey E. Koposov
Sternberg Astronomical Institute, Moscow University (Russia)
Max-Planck Institute for Astronomy (Germany) 
Internet: math@sai.msu.ru, http://lnfm1.sai.msu.su/~math/