physicsjs-collision-bug

Physics({ timestep: 4 }, function (world) {

    var viewWidth = window.innerWidth
        ,viewHeight = window.innerHeight
        ,edgeBounce
        ,renderer
        ;

    // create a renderer
    renderer = Physics.renderer('canvas', {
        el: 'viewport'
        ,width: viewWidth
        ,height: viewHeight
    });

    // add the renderer
    world.add(renderer);
    // render on each step
    world.on('step', function () {
        world.render();
    });

    // resize events
    window.addEventListener('resize', function () {

        viewWidth = window.innerWidth;
        viewHeight = window.innerHeight;

        renderer.el.width = viewWidth;
        renderer.el.height = viewHeight;
    }, true);

    function random( min, max ){
        return (Math.random() * (max-min) + min)|0
    }

    function dropInBody(){

        var body;

        body = Physics.body('rectangle', {
            width: 50
            ,height: 50
            ,x: (viewWidth / 2)
            ,y: 50
            ,vx: 0
            ,vy: 2
            ,restitution: 0.9
            ,styles: {
                fillStyle: '#d33682'
                ,angleIndicator: '#751b4b'
            }
        });

        world.add( body );
    }
    
    var bottom = Physics.body('convex-polygon', {
        vertices: [{x: 0, y: 500},{x: 0, y: 498},{x: viewWidth, y:498},{x:viewWidth, y:500}],
        x: viewWidth/2,
        y: 499,
        treatment: 'static'
    })
    
    world.add(bottom)

    var int = setInterval(function(){
        if ( world._bodies.length > 40 ){
            clearInterval( int );
        }
        dropInBody();
    }, 700);


    // add things to the world
    world.add([
        Physics.behavior('body-impulse-response')
        ,Physics.behavior('body-collision-detection')
        ,Physics.behavior('sweep-prune')
        ,edgeBounce
    ]);

    // subscribe to ticker to advance the simulation
    Physics.util.ticker.on(function( time ) {
        world.step( time );
    });

    // start the ticker
    Physics.util.ticker.start();
});