I keep reading notices and warnings in the official apps, for a productive system these messages should be logged and not displayed in public. In the worst case they give additional information away, information a potential attacker may use to compromise the system.
Example: (zensored)
Notice: Undefined offset: -2 in /****/app_index/CalendarRender.php on line 150
Example: (zensored)
Notice: Undefined offset: -2 in /****/app_index/CalendarRender.php on line 150