Bullet penetration is inconsistent and unclear

Some surfaces, though very thin and made of soft materials, cannot be shot though. This includes tarp, some fences, plywood, sheet metal, some windows, and other miscellaneous wooden or decorative objects. In other cases, objects that look identical to these bulletproof objects can indeed be shot through, like the wooden panels blocking the lower entrance to the B flag on Siege of Cairo. I believe this is a bug with certain materials in the game, and not intended design. You can tell when something has successfully been penetrated because there is a special icon for bullet penetration. I've seen it show up when shooting through bushes, other players, and the aforementioned wooden panels. This is part of why I believe that it's a bug that certain thin materials are bulletproof and not a design choice.