PiCamera python : buff/cache memory keeps increasing

Question

I need to take a picture in each second in an infinite loop. I've wrote 2 different python scripts: one with camera.capture() and another with camera.capture_continuous()

In both cases, I see the Buff/Cache memory keeps increasing until the maximum possible (after ~30 minutes).

When I stop the script, the memory stops increasing but doesn't decrease. The only way I've found to decrease the buff/cache memory to a level similar to before launching the script is to remove all the created jpeg files.... Do you have an idea from where is the memory leak? Is it already known?

Here is my code:

with PiCamera() as camera:
    # Picamera object / objet Picamera
    camera.resolution = (cmd['camera_resolution'][0],cmd['camera_resolution'][1])
    camera.iso = cmd['camera_iso']
    camera.start_preview()
    time.sleep(2)
    try:
        for i, image_filename in enumerate(camera.capture_continuous('image_{counter}.jpg', format='jpeg')):
        time.sleep(cmd['sleep_time'])
            if os.path.isfile(cmd['stopfile']):
                break
        camera.stop_preview()
        camera.close()
        sys.exit(0)
    except KeyboardInterrupt:
        camera.stop_preview()
        camera.close()
        print ('Quit')