Pullup Resistor Anomaly on Pin 13

I'm reading Pin 13 on a Leonardo board using the following code:

int val;

val = digitalRead(13);

Writing a low to an input should turn off any pull up resistors, so how come the LED on the board lights up when I read from input 13?

If there is nothing else connected to D13, it is floating. D13 connects to a high impedance op-amp to drive the LED. If you leave the input floating, the state of the output is not guaranteed. If D13 floats to a HIGH state, the LED lights.