The in-game description of this feat is incorrect. As per the Game Manual, this feat does not include attacks from hidden creatures. Successful attacks from stealth will not be affected by Uncanny Dodge.
Uncanny Dodge does work as described in the Game Manual and is only effective against invisible attackers.
Unlike 3.5, Uncanny Dodge will not be upgraded to Improved Uncanny Dodge, if a character with the feat gains it again from another class.