This has happened to me a couple days ago where it almost outdamaged my blackout kick. I have tried replicating the bug and the only possible outcome i could get was after going Brewmaster and using its abilities. I suspect it either came from Blackout Combo or the Face Palm artifact trait.
I reported it to Warcraftdevs already and I assumed it was fixed since my TP never broke past 35k at 840 ilvl average even after trying to replicate the bug again.
I tried it and I'm getting the same results. It comes from Blackout Combo in Brewmaster and then switching specs. First time I tried, I applied the buff, dropped combat, then switched to WW and all of my Tiger Palms were hitting for 50k non crit and 100k crits. I tried doing it again and it only worked on my first Tiger Palm, and then a third time it didn't work at all. It seems inconsistent but it's certainly coming from BM Blackout Combo and there might be a way to add in Face Palm as well like TrollShaman suggested.