civicrm.config.php didn't update after site move, causing Paypal Standard IPN error

I moved a site between two domains and updated the various settings files as instructed.

Paypal IPN didn't seem to be working, and checking
/administrator/components/com_civicrm/civicrm/extern/ipn.php
gave me an error referencing the civirm.config.php and an old path from the previous domain in it.

Going to /administrator/components/com_civicrm/civicrm/civicrm.config.php and changing the path to the new one fixed the problem - IPN works fine.

(NB - this is my first ticket, apologies if wrong. also not impossible I did something silly.)