After Diane and Pierce lock David in the closet and they both leave the bedroom, Diane still has her small gun in her hand. Immediately they meet the creepy boyfriend, but Diane no longer has the gun in her hand, nor is it anywhere else in the scene. If she had given it to Pierce, he would have used it in the climax scene when David was fighting the creepy boyfriend.
When David is reverting back to normal The Hulk is wearing a brown checkered shirt on the next close up he is wearing a blue shirt and so is the close up of David just before he turns back to normal.