And therein lies the problem. I was already using grayscale transparent-background PNG files. That's why this confuses me so much. As far as I can tell, there is absolutely nothing in the image (that's visible to me, anyway) that should be telling the game where the old frills are, yet that area gets filled with black.

I even tried copying everything into an entirely blank file just to see if there was some trace of something that was causing it in the original, but I still get the black original frills that shouldn't be there at all.

Thanks for all your help though! I really do appreciate it!