plpgsql: function throws error on second call!

hi,

i cant get it right on my own. i ve tried to find something in the
bug reports and there was a bug with temp tables in functions years
ago. but it was fixed..

so here s my problem:

CREATE FUNCTION testpunkte (int4) RETURNS int4 AS '
  DECLARE
    var_id ALIAS FOR $1;
    var_count int4 := 0;
  BEGIN

    CREATE TEMP TABLE temp_punkte AS
    SELECT * FROM tmp where id = var_id;

   UPDATE real
   SET    val1 = temp_punkte.val1
   WHERE  id   = temp_punkte.id;
   GET DIAGNOSTICS var_count = ROW_COUNT;
   DROP TABLE temp_punkte;

   RETURN var_count;
   END;
' language 'plpgsql';

it is just a dummy function on some testdata in my testdatabase
but if i call it two times:

testarea=# select testpunkte(1);
 testpunkte
------------
          1
(1 row)

fisrt time is fine and second time:

testarea=# select testpunkte(1);
NOTICE:  Error occurred while executing PL/pgSQL function testpunkte
NOTICE:  line 9 at SQL statement
ERROR:  Relation 7842984 does not exist

it seems to me the temp table is not generated in the second call of
the function.

but i dont know anything about system tables and so on so i cant
check it.

any hints or am i just stupid and dont see a typo?? but if the
function makes it right on the first call it cant be a typo.

hmm. looks strange to me. can anybody give me small hint, please?

kind regards
janning