Images sometimes won't show up in session browser

When browsing folders in a session, sometimes when I add a new photo (which shows in the finder in that folder), and browse to that folder in C1, it refuses to show up in the browser.  Then after a few days, it magically figures out life and shows in C1.  Very frustrating to work with.  This has happened multiple times recently.

Is there a trick to force C1 to 'refresh' the folder contents?