Nightmare puppeteer damage will often randomly trigger between its normal damage and another calculation that’s about -e22. Here when I set nightmare puppeteer to level 1 it deals below normal shadow clone damage.
The bug as far as I can tell only happens while barbaric fury is levelled and active tapping is happening, but also while fire sword and deadly strike are active (affecting the difference by about e20 and e2 each). but it is hard to test things exactly as it is random. I had fury at level 6 in this clip.
Edit: the difference between the -e22 and -e2 happening might be more to do with spell activation order or twilight fairies rather than fire sword or deadly strike