I manage several WordPress multisite installations in the domain educacion.navarra.es, each one with its own Akismet API key. In order to simplify their management, I use to hardcode the Akismet API key in wp-config.php file.
After updating Akismet plugin to version 2.5.8, the hardcoded key in wp-config.php file doesn't work. I've tried to hardcode it in akismet.php file, line 44, but to no avail. So, I've reverted to version 2.5.7.
Even in some normal sites (one blog installation), I have problems when the API key is hardcoded.
Any idea of the cause of this behaviour?