I've been thinking about your posts, Chrysanthemum, loves2 & Bookcase. You're all significantly more empathetic than me
I tend to see this sort of thing as manipulative, controlling and insulting - and say so rather promptly. I did live this for a while, and found it very unpleasant. As you've said, it seeks to invalidate you.
But ... each of you seems to be saying it stems from an inability to express bad feelings clearly, or a fear of expressing them.
I do recall a few occasions when I've handled passive-aggressive behaviour assertively.
Once was when XH and I had just moved in together. He stormed around the flat one morning, going "Haven't I got any clean shirts??!!?!" I enquired, sweetly, "I don't know, H, did you wash any?" He never tried that one again 
He was a big sulker, too. He could do it for weeks. I would go into a slightly insane pantomime mode, speaking to him as if we were having a normal conversation and then saying "Would you like me to ask that a different way? What do you think", etc, then carrying on as before. I was determined not to play the bloody game, but ended up behaving passively-aggressively myself despite my best intentions.
One of my SILs does the 'martyr' act a lot; I have found it very helpful to point out that she sounds angry, and ask her gently what she's angry about. She tends to get her stuff out after that, but I don't feel every martyr would respond as healthily.
I'm afraid that, after a childhood full of dumb insolence and life with my controlling Xs, I do passive-aggression rather too much myself. I work to express myself assertively but, frustratingly, find I'm now p-a against myself! 
I'm more than interested to hear everyone else's hints on dealing openly with these "hidden hits" and am following the links from your posts, Bookcase ...