This is not abnormal. There are designated market makers who are obliged to be at the best bid/ask some % of the time. If there are no bids, i assume they have no obligation (not sure). Secondly, even non-obligated MMs will watch the markets for good deals, but they won't always post orders for various reasons such as possibility of tieing up capital in less liquid contracts or to not give away their intentions, plus a variety of other reasons, it all depends. When you post a bid that is new information for them and they will act on it (new information about open intrest). If you mean that those bids stayed there after you got filled then it's possible it was an obligated MM that might need to keep those bids there so you screwed a little with their models maybe.
And when i say "watch the markets" that means they have computers that do that based on their pricing models, not real humans, like the poster before me suggested.