Drop-Down Menu not working on mobile devices

This worked for me:

$('.dropdown-toggle').click(function(e) {
  e.preventDefault();
  setTimeout($.proxy(function() {
    if ('ontouchstart' in document.documentElement) {
      $(this).siblings('.dropdown-backdrop').off().remove();
    }
  }, this), 0);
});

via robdodson on github

A temporary fix is to add

.dropdown-backdrop{
    position: static;
}

to the css file.

For me, it worked adding to my styles:

.dropdown-backdrop {
    z-index:0;
}

almost the same answer as Matthias, i hope it helps.