"past" and "future" CSS classes can be broken after using goto("#some-id")

Using goto can break the CSS classes "past" and "future". Here is some code to reproduce the problem on the current demo of impress.js :

    impress().init();
    impress().goto("bored");
    setTimeout(function() {
        impress().goto("ing");
        setTimeout(function() {
            var isPast = document.getElementById("step-2").classList.contains("past");
            console.log(isPast+ " should be true");
    	    var isFuture = document.getElementById("step-2").classList.contains("future");
    	    console.log(isFuture+ " should be false");
        }, 2000);
    }, 2000);