Pressing the "Serialize" button on the Sortable demo page in Opera 9.25 produces the following error:

JavaScript - http://ui.jquery.com/1.5a/demos/sortable.html 
Event thread: click 
Error: 
name: TypeError 
message: Statement on line 15: Could not convert undefined or null to 
object 
Backtrace: 
  Line 15 of linked script http://ui.jquery.com/1.5a/ui.sortable.js 
    return $.data(this, "ui-sortable").serialize(); 
  Line 1 of  script 
    alert($("#example1").sortable("serialize")); 
  At unknown location 
    [statement source code not available] 

Dragging the "and change" list item from the "3. Nested lists" demo 
produces the following error: 

JavaScript - http://ui.jquery.com/1.5a/demos/sortable.html 
Event thread: mousemove 
Error: 
Unhandled exception: [Object DOMException] 
code: 3 
message: HIERARCHY_REQUEST_ERR 
Backtrace: 
  Line 276 of linked script http://ui.jquery.com/1.5a/jquery.js 
    this.parentNode.insertBefore(elem, this.nextSibling); 
  Line 514 of linked script http://ui.jquery.com/1.5a/jquery.js 
    callback.call(obj, elem); 
  Line 725 of linked script http://ui.jquery.com/1.5a/jquery.js 
    for (var i = 0, length = object.length, value = object[0];i < 
length && callback.call(value, i, value) !== false;value = object[(+ 
+i)]) 
            Line 516 of linked script http://ui.jquery.com/1.5a/jquery.js 
    jQuery.each(elems, (function () 
{ 
  var elem = clone ? (jQuery(this).clone(true))[0] : this; 
  if (jQuery.nodeName(elem, "script")) 
    { 
      scripts = scripts.add(elem); 
    } 
  else 
    { 
      if (elem.nodeType == 1) 
        scripts = scripts.add(jQuery("script", elem).remove()); 
      callback.call(obj, elem); 
    } 
} 

)); 
  Line 725 of linked script http://ui.jquery.com/1.5a/jquery.js 
    for (var i = 0, length = object.length, value = object[0];i < 
length && callback.call(value, i, value) !== false;value = object[(+ 
+i)]) 
            Line 155 of linked script http://ui.jquery.com/1.5a/jquery.js 
    return jQuery.each(this, callback, args); 
  Line 485 of linked script http://ui.jquery.com/1.5a/jquery.js 
    return this.each((function () 
{ 
  if (! elems) 
    { 
      elems = jQuery.clean(args, this.ownerDocument); 
      if (reverse) 
        elems.reverse(); 
    } 
  var obj = this; 
  if (table && jQuery.nodeName(this, "table") && 
jQuery.nodeName(elems[0], "tr")) 
    obj = (this.getElementsByTagName("tbody"))[0] || 
this.appendChild(this.ownerDocument.createElement("tbody")); 
  var scripts = jQuery([]); 
  jQuery.each(elems, (function () 
{ 
  var elem = clone ? (jQuery(this).clone(true))[0] : this; 
  if (jQuery.nodeName(elem, "script")) 
    { 
      scripts = scripts.add(elem); 
    } 
  else 
    { 
      if (elem.nodeType == 1) 
        scripts = scripts.add(jQuery("script", elem).remove()); 
      callback.call(obj, elem); 
    } 
} 

)); 
  scripts.each(evalScript); 
} 

)); 
  Line 275 of linked script http://ui.jquery.com/1.5a/jquery.js 
    return this.domManip(arguments, false, true, (function (elem) 
{ 
  this.parentNode.insertBefore(elem, this.nextSibling); 
} 

)); 
  Line 298 of linked script http://ui.jquery.com/1.5a/ui.sortable.js 
    this.items[i].item[(this.direction == "down" ? "before" : "after")] 
(this.currentItem); 
  Line 137 of linked script http://ui.jquery.com/1.5a/ui.mouse.js 
    if (o.drag) 
      Line 101 of linked script http://ui.jquery.com/1.5a/ui.mouse.js 
    return self.drag.apply(self, arguments); 
  Line 2041 of linked script http://ui.jquery.com/1.5a/jquery.js 
    var ret = handler.apply(this, args); 
  Line 1839 of linked script http://ui.jquery.com/1.5a/jquery.js 
    val = jQuery.event.handle.apply(arguments.callee.elem, arguments); 
  At unknown location 
    [statement source code not available]