AJAX :: Odd Behavior On Setting Focus In User Control With Update Panel?

I'm having a bit of an issue in my ASP.Net application moving focus from a textbox in one user control to a text box in the next user control on the page after postback. I've searched high and low over the last several days to find a solution but, for whatever reason, have been unable to do so.

I have a page that has user controls loaded dynamically to allow a user to enter data.The number and type of user controls loaded to the page is determined at run time based on a database query.It is possible than many controls of the same type can be loaded. Each user control has its own update panel. Within the update panel of each control is a regular asp panel. Inside of the regular panel there are at least 2 server controls (any other controls that may exist in the user control are not affected by this issue) - a text box and a button.The defaultbutton property of the regular panel is set to the ID of the button within the user control. The desired behavior is to allow the user to enter data into the textbox on one user control hit enter to save the data on that user control the application will set focus to the textbox of the next user control on the page after the data from the "current" user control has been saved. Other considerations;

The application uses master pages. We make extensive use of ajax and the ajaxtoolkit in the application. I am using Visual Studio 2010 and .Net 4 The issue - when first entering the page, one can enter data into the first textbox and press the enter key. Data from "current" user control is correctly saved and focus is correctly moved to the next user control on the page.

Data can be entered into the textbox of "new" user control and when the enter key is pressed, the data is correctly save. The focus appears to move correctly to the next user control on the page.Data cannot be entered into the textbox of the control. Pressing the enter key will not save the data (because none was entered) but the focus will move to the textbox of the next user control on the page.

Data can be entered into the textbox of the user control. When the enter key is pressed, the data is correctly saved and the focus appears to move correctly to the textbox of the next control on the pageBasically, steps 3 and 4 are repeated until the end of the user controls on the page, alternating between being able to enter data and not. Other items of note When one is able to enter data into the textbox of a user control, one can correctly tab through the textboxes of each user control until the end of the page When one is not able to enter data into the textbox of a user control, pressing the tab key will take the focus to the address bar of the browser.

I created a much simplified example of the scenario described above and was able to consistently reproduce the "bad" focus behavior. All of the ajax toolkit controls and code where stripped out of the sample to rule the toolkit out as a cause. The behavior still occurs without the toolkit.

I am including the code for default.aspx and WebUserControl1.ascx.

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