Commonly referred to as bolting, this is a direct reaction to the application made. Like all living organisms, weeds exist to procreate and when survival is threatened, they will expend any existing energy stores into seed establishment. Many undesirable types of grass grow taller than the surrounding turf grasses in order to provide a reproductive advantage to the weed.
While this growth is not ideal, it is a sure indicator the plant is stressed and dying. Simply mow or trim the weed to a shorter height and say a eulogy over the poor thing!