Twitter bootstrap modal-backdrop doesn't disappear

Make sure you're not replacing the container containing the actual modal window when you're doing the AJAX request, because Bootstrap will not be able to find a reference to it when you try to close it. In your Ajax complete handler remove the modal and then replace the data.

If that doesn't work you can always force it to go away by doing the following:

$('#your-modal-id').modal('hide');
$('body').removeClass('modal-open');
$('.modal-backdrop').remove();

Make sure that your initial call to $.modal() to apply the modal behavior is not passing in more elements than you intended. If this happens, it will end up creating a modal instance, complete with backdrop element, for EACH element in the collection. Consequently, it might look like the backdrop has been left behind, when actually you're looking at one of the duplicates.

In my case, I was attempting to create the modal content on-the-fly with some code like this:

myModal = $('<div class="modal">...lots of HTML content here...</div><!-- end modal -->');
$('body').append(myModal);
myModal.modal();

Here, the HTML comment after the closing </div> tag meant that myModal was actually a jQuery collection of two elements - the div, and the comment. Both of them were dutifully turned into modals, each with its own backdrop element. Of course, the modal made out of the comment was invisible apart from the backdrop, so when I closed the real modal (the div) it looked like the background was left behind.

I just spent way too long on this problem :)

While the other answers provided are helpful and valid, it seemed a little messy to me to effectively recreate the modal hiding functionality from Bootstrap, so I found a cleaner solution.

The problem is that there are a chain of events that happen when you call

$("#myModal").modal('hide');
functionThatEndsUpDestroyingTheDOM()

When you then replace a bunch of HTML as the result of the AJAX request, the modal-hiding events don't finish. However, Bootstrap triggers an event when everything is finished, and you can hook into that like so:

$("#myModal").modal('hide').on('hidden.bs.modal', functionThatEndsUpDestroyingTheDOM);

Hope this is helpful!