This has always been a problem for me too. Kind of weirds me out. I had it at 160 pounds and I have it now at 200.
I wonder if it could be compensation for posture problems or unevenness. I think that's what it is in my case.
That could extend even to having one leg slightly longer than the other(which I have, and it raises one hip just a bit higher than the other, though I'm the only one who notices). Any structural imbalances will result in the whole rest of your body trying to compensate. It's a big job of your core muscles specifically to do that anyway, so they've got an even tougher and weirder job on hand if there are structural imbalances. That would tend to work one side of your support muscles like abs, low back, and obliques, a little more, and since you stand and sit up for so many hours each day for so many years, some small muscular uneveness could be pretty much expected, it would seem.
Unfortunately, this tends to suggest that changing your work-out won't change much, because your skeletal structure won't be changing, and you will ALWAYS have an uneven load on your support muscles. And that's a minute-by-minute for an entire lifetime thing that's of course longer and more profound than any work-out could ever be.
That's IF you have some small imbalance like me. It could also be postural bad habits with a perfectly balanced skeletal system(which might not be all that common) leading the core to unevenly certain support muscles. If that's the case, anything from chiropractic to Rolfing to yoga to simple attentiveness and discipline could go a long way toward evening things out.