This is one of the primary complaints with perpendicular slots, quite frankly. Due to the fact that the knives can slide against the wood when you remove them, it can end up damaging them. This is a fair issue to bring up but thankfully there is a way to get around it. Really, and this was alluded to in a previous question, all you need to do is store the cutting section of the blade upward. This way, the actual cutting section will never make contact with the wood.