The function is working :
Connect a LFO sawtooth on an inverted, then the inverted to a pitch modulation.  You will ear the different. 
Or use an oscilloscope to see the wave form. 
This later will show that a sawtooth inverted (down) is not very different in the audio range than a sawtooth (up). On is just a little (but very little) more "opened"
Best regards