Media browser contents do not update

If I have a document open in Pages, and open the Media Browser, I can view (among other things) the photos in my iPhoto library. If I then connect a camera and import photos into iPhoto, the Media Browser does not update to show the new photos. I usually have to quit and relaunch Pages, though every now and then something happens (I wish I knew what!) that magically causes the Media Browser to refresh without doing that.

Any clues? Is there a way to force the Media Browser to update its contents?