I've had the same thing happen on numerous quilts. I'm convinced it's related to fabric stretching, which happens even with the highest quality fabric. I don't take the time to 'unsew' the seams, and have found that once the quilt is washed, those tucks are much less noticeable.
Unless you're entering the quilt in a show, don't sweat it. Just enjoy the quilt, tucks & all! Good luck!