I ran into this last year. I was riding like a mofo, but my weight stagnated over the whole year on the same diet. I had lost 152 lbs. doing riding the bike and counting calories, but it suddenly stopped and plateaued. I tried to compensate by riding harder and more frequently, which just wore my body down but had no effect on my weight. I was stumped until I started doing some reading into the ideas like this.
This year I changed it up a bit. Cleaned up the diet, started lifting more weights and riding a whole lot less and the weight is starting to come off again.
At this point, I'm of the mind that successful weight loss is:
80% (or more) Diet
15% Resistance Training
5% Cardio Exercise
In the process of losing weight, I fell in love with cycling thinking that it allowed me to become health AND lose weight at the same time. I feel that is no longer true. Its great for health benefits and its also fun to do, so I will keep doing it for fun, just at a moderate pace now. But I'm no longer going to attempt to use it for weight loss by going harder, faster, further on the bike as that is a waste of time, imo.