Fixed #656.

dist/js/bootstrap-multiselect.js

@@ -447,7 +447,7 @@
             // Manually add button width if set.
             if (this.options.buttonWidth && this.options.buttonWidth !== 'auto') {
                 this.$button.css({
-                    'width' : this.options.buttonWidth,
+                    'width' : '100%', //this.options.buttonWidth,
                     'overflow' : 'hidden',
                     'text-overflow' : 'ellipsis'
                 });

index.html

@@ -1548,6 +1548,10 @@
                                         The width of the multiselect button may be fixed using this option.
                                     </p>
                                     
+                                    <p class="alert alert-info">
+                                        Actually, <code>buttonWidth</code> describes the width of the <code>.btn-group</code> container and the width of the <code>button</code> is set to <code>100%</code>.
+                                    </p>
+                                    
                                     <div class="example">
                                         <script type="text/javascript">
                                             $(document).ready(function() {