Try running this in java, you'll obtain 10 as output (autoboxing trap). Run the same in Groovy 1.7.5 will give you 2 as output

gistfile1.java

import java.util.HashSet;
import java.util.Set;

public class TestAutoboxing {

	public static void main(String[] args) {
		Set<Short> testSet = new HashSet<Short>();        
		short counter=0;
		while (counter<10)
		 {                    
		        testSet.add(counter);
		        testSet.remove(counter - 1);
		        counter++;
		}        
		System.out.println(testSet.size());	
	}

}

This will most probably change in 1.8