It just might be the last place you lose.
I've lost 15lbs and my calf and upper arm have only shrank 0.5".
i have the same thing going on, i was told by a trainer that i need to strengthen my back muscles to even out, because i have terrible posture and pathetic weak back muscles....he called it being "front heavy". also, i noticed that when walking, sitting, running....existing, i let my stomach settle and sometimes even PUSH OUT the muscles.....this, i'm pretty sure, has to do with my posture problem. consider if that's an issue for you, if so do a bunch of superman moves and flutter kicks on your stomach and just lift your lower body up.
I am a personal trainer and I absolutely agree with posts #2 and #3. The happiest day of my life was when my chiropractor said that I didn't need to lose weight, I just needed to stand up straight. An important muscle group to strengthen is the "T-A" or deep abdominal tissue. It's purpose is to prevent the back from over arching, and stabilize the pelvis and rib cage. Pilates is an excellent way to strengthen this muscle and "flatten" the belly, or any exercise where you suck in the tummy (I recommend sucking in your tummy as much as possible throughout the day, it trains the brain to hold better posture and strengthens the muscle)
Sadly, we all have problem squidgy parts, and fat or thin, your trouble spot will always be your trouble spot. THink J-Lo, in shape or outta shape, J-Lo 's got booty, that's how God her. Rejoice in your unique and beautiful shape.