2.5.2 error on combo box?

I just upgrade to 2.5.2, and found one of combo box function doesn't work. In 2.5.1, I used the following code to keep the selected item on the top of the popup list:

ddl.showPopup1 = ddl.showPopup;
ddl.showPopup = function(){
this.showPopup1();
this.getViewTemplate().element().parentNode.scrollTop = this.getCurrentItem()*16;
}

It worked fine in 2.5.1, but not work in 2.5.2. Shall I make some change?

Thanks,

Does it happen in IE or Firefox?

IE on XP