Frequency Modulation distortion in generated audio waveforms.

I’ve been working on an audio synthesis project and have noticed that when I change the frequency in real time, that the sound doesn’t change smoothly. It has a stepping through the notes as it changes. I’ve tried a smoothing algorithm, filtering, and oversampling to remove that distortion, all to no avail. Is there something in 4.13/4.14 that prevents this?