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.