Problems with jQuery Modal Dialogs problem can happen in a number of ways (see some of my other articles on the subject). This time, it was that I used a jQuery Modal Dialog inside of an ASP.NET UpdatePanel. After some looking around, what seems to be happening is that the dialog invisibly duplicates fields to the end of the document sent to the browser.
The best way of dealing with this poorly designed behavior of the jQuery Modal dialog widget is to just not use it if you are using asynchronous postbacks. I’ve had a number of problems with dialogs in the past, including random positioning issues on larger pages that I mentioned earlier.
There are a number of other options available as libraries, but it’s just as easy to style a hidden div to act like a modal dialog. This way it is your own code and you can handle things as you see fit. My experience has been that jQuery dialogs are easy to work with most of the time, but its when they mess up that they end up being a real headache.