I've found that as long as the polylines are reasonably regular C doesn't have a problem connecting things. The problems arise with irregular shapes where it tends to make a bad guess as to how to join the vertices. For the picture I drew a circle, duplicated it and raised the duplicate. Making a regular star shape caused no problems but this is the result of an irregular star. Use the link tool to joining the vertices how you want after cleaning things up. The vertex modeller is worth learning, especially if you want to export models to other apps. It is really very versitile and you have a lot of control. Stick with it!