e.force:showToast many times: order and max message onetime

Hi everyone, I want to show 4 error message onetime. But, I use the below code. First, 3 messages appear, when i close 1 message, 'message 1'   appears.

Can you explain me how it goes.

1. why cant show 4 message onetime

2. why message 1 was displayed lasted.

-----------code---------

showToast: function (type, message) {

        var toastEvent = $A.get("e.force:showToast");

        toastEvent.setParams({

            title : '',

            message: message,

            duration:' 5000',

            type: type

        });

        toastEvent.fire();

    }

showToast('error','message 1');

showToast('error','message 2');

showToast('error','message 3');

showToast('error','message 4');

Thanks.