the appendTo option should be a selector to a) prevent it from breaking, and b) match jQuery UI's API

Author: ehynds

src/jquery.multiselect.js

@@ -41,7 +41,7 @@
       autoOpen: false,
       multiple: true,
       position: {},
-      appendTo: document.body
+      appendTo: "body"
     },
 
     _create: function() {
@@ -69,7 +69,7 @@
         menu = (this.menu = $('<div />'))
           .addClass('ui-multiselect-menu ui-widget ui-widget-content ui-corner-all')
           .addClass(o.classes)
-          .appendTo(o.appendTo),
+          .appendTo($(o.appendTo)),
 
         header = (this.header = $('<div />'))
           .addClass('ui-widget-header ui-corner-all ui-multiselect-header ui-helper-clearfix')