MySQL Forums :: Triggers :: Trriger which converts characters

Hi,
I develope trigger which converts polish liters, remove spaces and return lowercase string into column "url".
My trigger executes correctly few times but until the moment I don't know why but it stop converts liters and remove spaces but trigger return lowercase string. When I drop and recreate this trigger it works perfect but still until the moment.
Source:
CREATE TRIGGER plurl BEFORE INSERT
ON artykul FOR EACH ROW
Begin
SET @a = replace(replace(replace(replace(replace(replace(replace(replace(replace(replace(
lower(new.nazwa),

'ą', 'a'), 'ś', 's'), 'ę', 'e'), 'ż', 'z'), 'ź', 'z'), 'ć', 'c'), 'ń', 'n'), 'ł', 'l'), 'ó', 'o'), ' ', '_');
set new.url = @a;
End;