I’m using Bootstrap 3.0 (hopefully, this works with 3.1 as well).
We had to use tabindex="-1"
because that allows the ESC key to close the modal.
So I was able to fix this issue using:
// Every time a modal is shown, if it has an autofocus element, focus on it.
$('.modal').on('shown.bs.modal', function() {
$(this).find('[autofocus]').focus();
});