Leaking HOTPOINT Aquarius dishwasher?

I have a HOTPOINT Aquarius Super7823 Dishwasher. To the bottom right hand side of the water intake syphon system there appears to be a designed hole. When the dishwasher fills it does it via tree cycles. On the first two cycles the water level approaches this hole but does not quite reach it. On the third cycle it reaches it and overflows, only about 5ml but its enough. Is this hole part of the design or is it normally plugged by a plug that has come detached. There seems to be hole to the back of the first so a normal plug (cork) would not suffice, it would need to be of exact dimentions. Why would you have a hole in this position.