Odd behavior on ADC, please help!

Other Hardware General Electronics
12

I'm starting to consider the possibility of a bug within the arduino hardware or IDE (compiler).
I ran tests similar to suggested ones on this thread, and it turns out I can turn on all 12 lights without affecting the ADC if I don't use if statements using the following code:

void loop() 
{  
  int sensorValue = analogRead(A1);  
    
  digitalWrite(2, HIGH); digitalWrite(3, HIGH); digitalWrite(4, HIGH);
  digitalWrite(5, HIGH); digitalWrite(6, HIGH); digitalWrite(7, HIGH);
  digitalWrite(8, HIGH); digitalWrite(9, HIGH); digitalWrite(10, HIGH);  
  digitalWrite(11, HIGH); digitalWrite(12, HIGH); digitalWrite(13, HIGH);  
  delay(1);
}

When I'm sampling the audio signal but ignoring it, I can do whatever I want with the lights and the ADC does not exhibit the odd going-high behavior described in the original post. Can it have something to do with the if statements?

Thank you all for your interest and suggestions.