The lemon seems like the likely culprit, in hindsight.
I checked some online recipes, and lemon juice is added at the end in several. My original recipe has meat tenderizer and lemon juice kneaded into slashes in chicken prior to applying the marinade. I leave out the tenderizer (even on chicken), but kept the lemon.
It made a passable shrimp salad today: chilled down they're a little more solid, with some more yogurt, cayenne, cumin and cardamom, put on whole wheat Ritz crackers it was pretty darn good.
What is patriotism, but the love of good things we ate in our childhood?
-- Lin Yutang