Pre-1.2 Flame Sweep did not add stacks to PFT unless it hit someone (to my irritation). However, I noticed yesterday that it added stacks even if I didn't hit someone. It's quite handy in order to not drop stacks between fights.
Hmmm, guess I should probably give it a try. I had basically found myself never using Flame Sweep because it's energy cost was high, and using it for one stack was kind of annoying. I will test it out this afternoon and see if it works. If it does than I am guessing it's an unintended bug.