To replicate (and test):

1. Install APC and the APC cache store.
2. Enable APC in your php.ini and restart your webserver.
3. Create an APC instance, and map it to the application cache mode.
4. Visit the home page and ensure it is operating.
5. Disable APC in your php.ini and restart your webserver.
6. Browse to your sites frontpage, ensure you don't get errors and that the APC store isn't being used.