ah yes, I've seen the negative D as well, building both legions and synthetic pop, though not a big deal for D as it will replenish
food is not a resource like D or the others though - it is static and global and only needed to BUILD a city, not maintain it.
I don't mind negative food not having a penalty, I do agree that it would be a cool addition.
think of it like this ... cities are always self-sustaining when built. The population builds roof gardens, or the government subsidizes crops. The food is only needed until the city is self-sustaining (built). It is not a bug, it is not a big deal.