Problem with records that disappear.

Hello,

from some time I have a very strange problem with my postgresql 9.2.2
64bit.
I make a few changes with an plp function:

BEGIN
   UPDATE table SET X = X where id = aid;
   UPDATE table_2 SET Y=Y where id = aid;
   IF aid > 0 THEN
     SELECT INTO ids id FROM table_3 WHERE x = x;
     IF aid IS NULL THEN
       INSERT INTO table_3 (id) VALUES (x);
     ELSE
       UPDATE table_3 SET id = id + 1 WHERE x = X;
     END IF;
   END IF;
   RETURN 200;
END;


When I call the function from php everything it's seems to work,
but some time modify records just disappear. I don't have any ideas for
the moment
what is the problem in my postgresql or in my php code. I'm sure there
was a recording was made.
I run in middle night vacuum, reindex on tables and vacuum analyze;
I check my postgresql logs, but no any errors. I check the php logs,
but no errors.
My vacuum also did not log any error messages. This problem happened
one or two times per month
and I can't track him. Is not happened very often. My question is: Is
there any chance this function
to stay opened or some thing like that and on the night when vacuum is
started to rollback changes ?
Also any other suggestions are welcome.

Cheers,
Hristo C.