New maps have some shoddy modelling and texturing: some rooftops have ledge textures that extend further out than the actual roof/ledge model so you can easily fall through the texture if you are wiggling around in prone trying to line up a shot. Also some corners of buildings are extra thick, but the extra thickness is an invisible part of the model so when you for instance throw a grenade, trying to line it up so that you don't have to get that much out of cover when throwing, the grenade bounces off the invisible extension.