Modal is "remembering" code from previous modals

The Problem is you only set new src values but the image-elements themselves (which are hidden/displayed after a click on the thumbnails) are still in the same state as in the modal before.

I got it working by triggering a click on the first thumb when the modal opens:

open: function() {
    correspondingModal.find("#thumb_1").parent("a").trigger("click");
}

Updated Fiddle

Could be a hackjob. But have a try. Add this piece of code in the click of .info function:

$(".content img").hide(0, function () {
    $(".image_1").show();
});

This effectively "resets" the images:

Fiddle: http://jsfiddle.net/praveenscience/nLhcejsz/2/

I changed the order of your inital .ready() functions and attempted to save the contents of all modals and reload them when Custombox is closed.

EDIT: The non-loading images has been resolved by loading the content on both the open() and close() functions of Custombox.

Grab initial modal content:

$(".modal").each(function () {
    window['reset' + $(this).attr('id')] = $(this).find('.content').html();
});

Load modal at Custombox open():

open: function(){
            $(".modal").each(function () {
                $(this).find('.content').html(window['reset' + $(this).attr('id')]);
            });
        }

Reload modal at Custombox close():

close: function(){
            $(".modal").each(function () {
                $(this).find('.content').html(window['reset' + $(this).attr('id')]);
            });
        }

UPDATED FIDDLE: http://jsfiddle.net/nLhcejsz/6/

This should now behave as you are requesting, the modal forgets which thumbnail was clicked and resets accordingly.