I'm experiencing a weird problem related to RadAjaxManager on a SharePoint 2103 layout page. From time to time (it seems quite random) "ajaxified" buttons (i.e. the ones under control of RadAjaxManager) issue a full postback instead of a partial AJAX request. As a result, values entered on a form (in text boxes, drop-down lists etc) are lost because the entire page is pull out from the server. This is a really bad user experience.
I did my research and it seems that disabling Forms Authentication in IIS of my SharePoint web application fixes the issue. The question is why does it fix the problem? I don't understand how RadAjaxManager can be related to Forms Authentication. I have to explain that to my client.