I think that it wont render anyting there, and a "passing over stay" effect will occour. Everything that was rendered on that perticular pixel last time wont dissapear. So if you reload your weapon in front of it, it will create trails from freeman's hand and his weapon. But im not sure, make a boxmap and try it out.

(the answer is no, it won't cause a leak- in fact, you should place nodraw brushes behind displacement surfaces on the edge of your map to seal it- Lep.)