Sometimes when I am shooting a silenced weapon especially when I shoot it in long burst (whole clip) and in close range. It seems as though the gun stops shooting. I am still holding down the trigger but I don't hear the gun firing anymore. This usually happens in a close range fire-fight so I don't have time to check the status of my clip.
It happens to me occasionally. Look at your weapon while you are firing to see if you are still ejecting empty casings. This is mostly a sound glitch, so you should still be fine.
__________________
"DO UNTO OTHERS AS YOU WOULD HAVE THEM DO UNTO YOU."
It happens because the silenced noise is drown out by the noise of the bullets hitting the ground or wall and that just takes the sound away until you start shooting at something farther away. It's a dumb glitch. But as long as your reticle is bouncing or moving your still firing.