Let's get Jay Sandhu to weigh in on this again, but perhaps you could provide more details (like screen shots) of your problem. While I'm not as active in NA as I used to be, it's been my experience that service area polygons are more of a guideline than a hard, fast boundary. What really matters is how the routes themselves show up as the service area.
What software/version are you using and what settings are you using for the service area. As Joe mentioned, post a picture of a problem and that might help figure out change in settings.