It's just how it works, though not always ideal for non-truckers, either.
Once you are within proximity of a waypoint, the device determines that waypoint to have been 'visited', and starts you on your way to the next one. Again, the problem isn't just for truckers. Imagine driving in a downtown area in any vehicle, lots of one-way streets, not much parking, plenty of traffic -- and you have to pass in front of your destination while you search for some place to park. As you pass by, the route to the next waypoint pops up, and you're still trying to figure out how to circle around the one way streets looking for someplace to park near your current destination again. Not fun. I think this is what you're talking about.
The only solution I've ever found to that is to keep hitting 'recent destination', which isn't always very convenient while you're navigating in downtown traffic.
One thing I've requested in the past, though it hasn't been implemented, is that in urban areas, the 'visited' proximity be shortened so that it's necessary to be closer to the waypoint before it's declared 'visited'. That would help in some cases, at least.