If you look in the documentation (6.0 or later IDEs have this section, it might not be in 5.0 and earlier documentation even though I think it applies there too) at the index entry for "synchronization", you find the following particularly relevant part:

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We also recommend configuring the HTTP server to give short expiration times to Curl applets, but not to other files loaded directly or indirectly by the applet. The Curl RTE can make sure that the files it loads are synchronized according to the applet's resync-as-of declaration, but has no control over the synchronization of the applet file itself since that is controlled by the web browser. The end-user can force synchronization in the browser by holding down either Control (for IE) or Shift (for Netscape/Mozilla) when pressing the reload button (usually mapped to the F5 key), but that requires the end user to know when to do that. The expiration period depends on the nature of your application, but unless the applet is very large and you do not need users to notice changes quickly, it usually makes sense to expire it immediately. Setting expirations for other files used by the applet is not recommended because it will result in extra unnecessary HTTP synchronization.

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So you do need to make some web server settings to make the caching and synchronization work best.