Whenever you have a problem that Flex Builder / Flash Builder won't build / compile your Flex application (e.g. you are seing the "stale" version which is doing other stuff than your source code, breakpoints don't match etc.) try clearing the browser cache.

If you use Firebug, check Net > Disable Browser Cache.

Or you can, alternatively, go to about:config and set browser.cache.disk.enable = false.

Or this: network.http.use-cache = false.

Since this disables caching on a browser level, some people are suggesting concatenating the random suffix to your SWF path inside the HTML wrapper file to avoid caching.