It's a bit more subtle than that.

  i += i++;
  Console.write(i);

could print 0, 1, or 2 depending on the order in which

  i++

and

  i += <value>

is evaluated. From the winning answer, what's really happening is:

  int i = 0;
  i = i + i;
  i + 1; // Note that you are discarding the calculation result

This kind of nonsense is the reason why Python doesn't have prefix and postfix increments.