I had a login form -- two rad text boxes and a button -- and was calling LoginIdRadTextBox.Focus() in the code behind (Page_PreRender).
The TabIndex for the controls (login, password, button) was set explicitly in the markup as 10, 20 , 30 respectively. This form was used in production for some time, but with the latest release (2008.3.1105.20) the behavior changed. Instead of tabbing from the LoginIdRadTextBox to the PasswordRadTextBox, pressing tab would instead take you to the address bar.
I found that the Focus() method wasn't working reliably in some browsers anyway, so I killed two birds with one stone by replacing the call to Focus() in the code-behind with this:
Telerik.Web.UI.RadScriptManager.RegisterStartupScript(Page,
GetType(Page), "Focus", String.Format("window.setTimeout(""document.getElementById('{0}_text').focus()"", 300);", LoginIdRadTextBox.ClientID), True)
In working toward this solution, I also tried using RadAjaxManager.FocusControl() but that wouldn't work either. I didn't want to create a case because I have the work-around above, but in future releases I'd like to see tabbing/enter key behavior in a form work exactly as it does without the decoration (I had to employ yet another work around for enter key behavior).