Map does not clip to size.

[mbostock]

If the map size is bigger than its container, the map does not clip. This can cause image tiles to extend beyond the edge of the map. We can detect when the map size is set explicitly (size is non-null), and then add some appropriate clipping to the map container.

[mbostock]

I'm closing this as not a bug, because it's fairly easy for the user to introduce their own clipping on the map container. Furthermore, the user might not want clipping, or might want to use a different clipping shape (such as a circle or an arbitrary path). If needed we could reopen this as a feature request for the map to support automatic clipping on its container.