** Huge performance and usability improvements on SHIFT + click multi-selection **

-> Now able to select/deselect ranges
-> The range is based on the previously active checkbox. (i.e: the user clicks a checkbox no 1 then checkbox no 5. The interval will be [1,5].)
-> The range new state (selected or deselected) depends on the last option clicked new value. Example: If the checkbox is Shift-clicked and becomes selected, the whole range will be too.
-> Improved the range select speed tremendously by only notifying the select for the "change" event once the whole range finished changing and manually doing the selection or deselection.

dist/js/bootstrap-multiselect.js

@@ -99,6 +99,7 @@
         this.originalOptions = this.$select.clone()[0].options;
         this.query = '';
         this.searchTimeout = null;
+        this.lastToggledInput = null
 
         this.options.multiple = this.$select.attr('multiple') === "multiple";
         this.options.onChange = $.proxy(this.options.onChange, this);
@@ -458,48 +459,62 @@
                 }
             });
         
-            $('li a', this.$ul).on('touchstart click', function(event) {
+            $('li a', this.$ul).on('touchstart click', $.proxy(function(event) {
                 event.stopPropagation();
 
                 var $target = $(event.target);
                 
-                if (event.shiftKey) {
+                if (event.shiftKey && this.options.multiple) {
                     if($target.is("label")){ // Handles checkbox selection manually (see https://github.com/davidstutz/bootstrap-multiselect/issues/431)
                         event.preventDefault();
-                        $target = $(this).find("input");
-                        $target.prop("checked", !$target.prop("checked")).trigger("change");
+                        $target = $target.find("input");
+                        $target.prop("checked", !$target.prop("checked"));
                     }
                     var checked = $target.prop('checked') || false;
 
-                    if (checked) {
-                        var prev = $target.closest('li')
-                            .siblings('li[class="active"]:first');
-
-                        var currentIdx = $target.closest('li')
-                            .index();
-                        var prevIdx = prev.index();
+                    if (this.lastToggledInput !== null && this.lastToggledInput !== $target) { // Make sure we actually have a range
+                        var from = $target.closest("li").index();
+                        var to = this.lastToggledInput.closest("li").index();
                         
-                        if (currentIdx > prevIdx) {
-                            $target.closest("li").prevUntil(prev).each(
-                                function() {
-                                    $(this).find("input:first").prop("checked", true)
-                                        .trigger("change");
+                        if (from > to) { // Swap the indices
+                            var tmp = to;
+                            to = from;
+                            from = tmp;
                         }
-                            );
+                        
+                        // Make sure we grab all elements since slice excludes the last index
+                        ++to;
+                        
+                        // Change the checkboxes and underlying options
+                        var range = this.$ul.find("li").slice(from, to).find("input");
+                        
+                        range.prop('checked', checked);
+                        
+                        if (this.options.selectedClass) {
+                            range.closest('li')
+                                .toggleClass(this.options.selectedClass, checked);
                         }
-                        else {
-                            $target.closest("li").nextUntil(prev).each(
-                                function() {
-                                    $(this).find("input:first").prop("checked", true)
-                                        .trigger("change");
+                        
+                        for (var i = 0, j = range.length; i < j; i++) {
+                            var $checkbox = $(range[i]);
+
+                            var $option = this.getOptionByValue($checkbox.val());
+
+                            $option.prop('selected', checked);
                         }                   
-                            );
                     }
+                    
+                    // Trigger the select "change" event
+                    $target.trigger("change");
                 }
+                
+                // Remembers last clicked option
+                if($target.is("input") && !$target.closest("li").is(".multiselect-item")){
+                    this.lastToggledInput = $target;
                 }
 
                 $target.blur();
-            });
+            }, this));
 
             // Keyboard support.
             this.$container.off('keydown.multiselect').on('keydown.multiselect', $.proxy(function(event) {