I also had some trouble with my scrollable modals, so I did something like this:
$('.modal').on('shown.bs.modal', function () {
$('body').addClass('modal-open');
// BS adds some padding-right to acomodate the scrollbar at right
$('body').removeAttr('style');
})
$(".modal [data-toggle='modal']").click(function(){
$(this).closest(".modal").modal('hide');
});
It will serve for any modal whithin a modal that comes to appear. Note that the first its closed so the second can appear. No changes in the Bootstrap structure.