Size of PriorityQueue increases when a non-comparable object is added

Consider the following code:

import java.util.PriorityQueue;

public class Test {

    public static void main(String argv[]) {
        PriorityQueue<A> queue = new PriorityQueue<>();
        System.out.println("Size of queue is " + queue.size()); // prints 0
        try {
            queue.add(new A());
        } catch (ClassCastException ignored) { }
        System.out.println("Size of queue is " + queue.size()); // prints 1
    }

} 
class A { } // non-comparable object

In this code, an object, which is explicitly non-comparable, is added to a PriorityQueue. As expected per PriorityQueue.add Javadoc, this code throws a ClassCastException because the object is not comparable.

However, it seems that the size of the queue is still increased, although an exception was thrown.

I would have expected both print statements to output 0 but the second one actually outputs 1, as if an object had been added to the queue.

I find this really strange, is this behaviour expected? If so, what is the reason behind this and where is it documented? I can't find anything related to this.

via Chebli Mohamed