Why does a rabbit stand in there food?

I've had my Minnie Lop eared rabbit for about 1 1/2 months. I have a Male and a female and they're both sweet. But for some reason they always stand in their food and knock the dish over! I've asked some people on why they do this, but they also have no answer to this. Or, my bun-bun's will grab their food dish with their teeth and pull it and knock it over. When they do spill out their food, should I also refill, or should I not since would that be a waist of rabbit pellets? Please help!