Java strange behaviour : elapsed time is faster with println

Question

I'm seeing some strange behaviour in Java:
Commenting a println makes the function execute slower.
Uncommenting the println makes the function execute faster.

I would expect this to be reversed, as println should cost time.

The trigger is the System.out.println(""); in the sequentialProcessData function.
With the line commented I get 2.5 secs.
With the line uncommented I get 1.9 secs.

The behaviour is independent of using nanotime() or currentTimeMillis() to measure time.

Also, I could not reproduce the behaviour when triggering the println with a flag.

Tested with Eclipse, jdk1.7.0_51 (JavaSE), Windows 7 (8 cores in case that matters).

Thanks

EDIT
This behaviour only occurs for me when I compile the code in Eclipse. (running in Eclipse and in the shell both have this strange behaviour)
If I compile in the shell (javac Main.java), then the behaviour is normal, i.e. the println version is slower (by about 1 secs).

So something strange with the Eclipse compiler?

Code:

import java.util.Random;

public class Main {

  public static void main(String[] args) {

    // Generate Data Matrix with random numbers
    int ROWS = 10000;
    int COLS = 40;
    double[][] data = generateData(ROWS,COLS);

    //Variables
    long start_main;
    long end_main;

    // Time consuming function
    start_main = System.nanoTime();

    sequencialProcessData(data);

    end_main = System.nanoTime();
    System.out.println("main duration: " + (end_main - start_main)*Math.pow(10, -9) + " secs");

  }

  static double[][] sequencialProcessData(double[][] data) {

    double[][] result = new double[data.length][data[0].length];

    for(int col = 0; col < data.length; ++col) {
      for(int row = 0; row < data[col].length; ++row) {
        for(int i = 0; i <= row; ++i) {
          result[col][row] += data[col][i]; 
        }
      }
    }

    // TRIGGER : COMMENT and UNCOMMENT THIS to see a difference in performance
//    System.out.println("");

    return result;
  }

  static double[][] generateData(int ROWS,int COLS) {

    double[][] data = new double[COLS][ROWS];

    Random random = new Random();
    for(int col = 0; col < COLS; ++col) {
      for(int row = 0; row < ROWS; ++row) {
        data[col][row] = random.nextDouble();
      }
    }

    return data;
  }

}