trigger problem (wrong results)

Hi list!
I pretty newbie in using triggers ,so sorry if this is a known thing.
I was trying to count rows in several tables by one of its column for
example i have :

          Table "schedule"
 Column    |         Type          | Modifiers
--------------+-----------------------+-----------
 studentid    | numeric(9,0)          |
 groupid      | numeric(10,0)         |
Triggers: schedule_rashum_decrcounter_tr,
          schedule_rashum_incrcount_tr,

     Table "public.counter"
    Column    |         Type          | Modifiers
--------------+-----------------------+-----------
 counter_type | character varying(30) |           --the name of the table we are counting
 ident        | numeric(10,0)         |           --a column from the target table
 count        | integer               |

When a new student is inserted into the group i want to have the count for that group
to be increased, so i would increase the count in the row where ident = groupid and
counter_type='schedule'.
If the row in the counter does not exists yet, i should create it.
Here is the trigger:

create trigger schedule_incrcount_tr after insert on schedule
for each row execute procedure incrcounter ('schedule');

create trigger schedule_decrcounter_tr  before delete on schedule
for each row execute procedure decrcounter ('schedule');

create or replace function incrcounter()  returns trigger as'
DECLARE
        input_refc              refcursor;
        qRes             record;
        q                text;
        ident            text;
        tableName        text;
BEGIN
        tableName :=     TG_ARGV[0];
        IF tableName = ''schedule'' THEN
                ident :=  NEW.groupid;
        END IF;
        q := ''SELECT * FROM counter WHERE counter_type= '' || '''''''' || tableName || '''''''' ||  '' and ident='' ||
ident; 

        OPEN input_refc FOR EXECUTE q;
        FETCH input_refc INTO  qRes;
        CLOSE input_refc;

        IF FOUND THEN
                EXECUTE ''UPDATE counter SET count=count+1 WHERE counter_type= '' || '''''''' || tableName || ''''''''
|| '' and ident='' || ident ; 
        ELSE
                EXECUTE ''INSERT INTO counter (counter_type,ident,count) VALUES ( '' || '''''''' || tableName ||
''''''''|| '','' || ident || '','' || 1   || '' ) '' ; 
        END IF;
        RETURN NEW;
END;
'LANGUAGE 'plpgsql' ;
The decrcounter is pretty the same except that in does counter=counter-1.
Obviously i have forgotten the 'for update' in the first select but those locks are done in the
application.
When trying the trigger all works fine but after using it on live application
i have some of the numbers wrong .The numbers are so terribly wrong that i can't explain it as a
transaction (concurrency) problem or something.
Please help ,what am i missing?
Many thanks .
Evgeny.