I just completed the "Fake Papers" quest in Velen with the merchant who wants you to protect his brother clearing a battlefield. I returned to him for his "discount" and no matter which option I choose it says "Quest completed!" then shortly thereafter in red "Quest Failed!" and a new Failed Quests tab opens in the Quest log but it does not show any failed quests. In fact, the Fake Papers quest just completely disappears from the quest log not to appear anywhere completed or failed.

Anyone else encountered this? Known bug perhaps? Not sure what the repercussions of this are.

Mmh definately sounds like a bug.
I completed the battlefield quest before and as the man asked me to do it Geralt just said something like "Oh, well, I already did this". The quest completed and I got the discount.

Later on I saved and exited the game and when I reloaded my game afterword the quest showed up as failed because the guy's brother died in the battle. I probably should not have started the quest at level 4 even though I killed everything, it took longer for me to kill everything and that left the guy more vulnerable I guess. Just a game of choices and consequences it seems. There's another way to get a pass though apparently so I'll have to slug it out until I get that far. :)

I'm now on the quest to meet some elf mage in an underground cavern with the witch chick.