I've heard of this on centerboard boats, but not on a laser before. What it means though is that the back of the daggerboard isn't sealing well with the hull, and there is a considerable space in the back. I wouldn't worry about it much, but if it bothers you, you can tighten the rubber daggerboard stop.
I get this only when flying downwind and bouncing around on waves with centreboard half up. I'm going so fast and there is normally so much other water splashing about that a little extra coming up through the case doesn't seem to matter much. The Laser doesn't have a gasket between the hull and board so I can't really see a way of stopping it.
The water coming through the trunk is a good thing. A few years ago I took my young Golden Retriever for a ride. He was extremely uncomfortable about the entire process UNTIL...
He noticed the water coming in and realized he could try to bite that water. Then he discovered that the water sometimes splashed over the top of the deck and biting that water became a full time occupation.
The only downside was the relationship between the claws attached to his dancing paws and my shins.
And the two of us total over 150 kg so the boat really does not sail well when he is riding along.