ModalPopupExtender strange behavior

I'm developing an ASP.NET application with C# and Visual Studio 2008 SP1. I'm using WebForms.

I have an ASPX page with two UpdatePanels, one on the left that holds a TreeView and other on the right where I load dynamically user controls.

On the left panel I also have buttons to load user controls on the right. I have a ModalPopupExtender in a button that show I div with radiobuttons to select a type. When I choose an option and click ok it do a postback to load dynamically a user control but instead of 开发者_Python百科dissapear these modal panel it appers on the bottom left corner of the page.

What's happening? I think it is about dynamic load.

It is a bug on AjaxControlToolkit. I've decided to use the following answer: jQuery UI's Dialog doesn't work on ASP.NET