I am absolutly postively 100% sure that i have seen NPC's throw grenades through walls. Both time occured in the RMG one of the buildings. I'll describe the first time it happened. I'm on the first floor in this one room. There are stairs on the other side of the room. There is an enemy on the stairs, on the other side of the room.  I'm camping in the corner waiting for him to go down the stairs and in front of the doorway so i can bleast him. Well i'm waiting when something catches the corner of my eye. I turn to see what it is just like anyone else would. Well rememeber how i said and enemy was on the stairs which is next to the room. I see his hand go through the wall, honest truth, drop the grenade on the ground, and his hand goes back through the wall. This has happened several times, all in similar situations. I'm not flaming anyone but i'm just reporting what i've seen. Also - i thought the ai wasn't supposed to "see" me through walls anymore, but they still do.