class Database_PDO_Connection extends \Fuel\Core\Database_PDO_Connection
Again, this was working fine in 1.3. Also, when I try to rename the path to something else like __DIR__.'/this/is/an/invalid_path.php' I don't receive an ErrorException of No such file or directory. Other classes are loaded properly and extends and replaces the core's.
Wow, this is very weird. Suddenly found my old apps to not work as well.
Tried changing my sessions.php config to use cookies instead of the database and got it to work again. Is there another way for Database_PDO_Connection to work even with sessions using the database instead of cookies?
I don't have any issues with database connections here whatsoever.
When did you install 1.4? And what is in your app/config/db.php? If it's empty, check core/config/db.php, the initial master repo had a bug in which the example mysql config would overwrite the PDO config. If so, remove the mysqli part.
That will cause a connection failure, but is not related to a class extension issue.