This is not a bug because no body else has ever reported this issue.
It is more likely the behavior of the pin is different from what you expect. So let's look at your code.
Porlune:
void setup() {
// initialize the digital pin as an output.
Serial.begin(9600);
Serial.println(PORTB); //prints 0
pinMode(led, OUTPUT);
bitClear(PORTB, 5); //turns ON led connected to pin 11
Serial.println(PORTB); //prints 0
}
If the cathode of the LED is connected to the pin (through a current limited resistor) and the anode is connected 5V, this could turn on the LED.
This is, of course, assuming that "led" is set to 11. That part is missing in your code. Which is troubling. You're describing a behavior that nobody else experiences but you have yet to: a) explain exactly how your hardware is connected and b) post proper code.