Zooming the Map Control to a Bounding Box

Base on what I have read in the documentation I should be able to create a bounding box and a number of coordinates to it and then set the map control to use it as the zoom with a buffer around the box. When I do this it simply zooms to the last coordinate added to the bounding box. Am I missing something?

Simplified Like this:
BoundingBox bb = new BoundingBox();
foreach (LatLon Coordinate in <List of Coordinates>)
{
bb.Add(Coordinate);
}
mapCtrl1.Map.ZoomToBoundingBox(bb, 10);
mapCtrl1.Invalidate();