Ok, it seems to work on my setup with a Pot on A0, but I have no idea why. A0 is defined as 14.
Analog input pins float all over the place unless they are connected, so getting a number when you disconnect does not mean a whole lot. That's the reason you need to have pull down/up resistors when you connect switch type devices.
Recheck your circuit. If you are using a breadboard, take a photo and post it or attach it to the posting.