I just bought a G17 Gen 4 and noticed an unusual protrusion at the rear of the frame, just below the slide. It appears to be intentional; it doesn't look like a mistake with the molding or manufacture. My G19 and G34 (both Gen 4s) do NOT have such a bump on the back. Any ideas? (See the lousy cell phone pics below.) Thanks in advance. Wanna kill these ads? We can help!