Symfony2 dev environment not clearing cache automatically

I'm working on a new Symfony2 project, and I'm using the app_dev frontcontroller to view the default AcmeDemoBundle's pages.

When I make changes to the controllers, I get an exception (NotFoundHttpException: No route found for "GET /demo/hello/World"). If I clear the cache using php a开发者_开发问答pp/console cache:clear, things work great again. However, it is my understanding that by using the app_dev front controller, I shouldn't be required to do this. Am I doing something wrong?

Soms system specs: OSX Lion using MAMP PHP 5.3.6 Symfony 2.0.1

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Are you using different users for webserver and command line user? Maybe you should check for permissions in the Setting up Permissions paragraph.