IQODE Limited

Recently I was working on a project that extensively used Telerik RadControls for ASP.Net AJAX and we were experiencing some Internet Explorer CSS rendering weirdness across versions 6,7 and 8 whenever an AJAX call was made. My immediate thought was the usual IE float clearing bug, a double margin bug or, let's be honest, one of any number of irritating IE CSS bugs . The strange thing was each IE version exhibited slightly different rendering issues which, after some thought, made me think it was something else.

After some rummaging around with the wonderful Firebug I noticed that all of the style sheets within the IE conditional comments were being attached after each AJAX callback. So the style sheet for IE6 was being attached when viewed in IE7 and IE8 and so on. Hmmm.

It seems that the RadAjaxManager doesn't handle IE conditional comments. After an Ajax request the RadAjaxManager attaches all style sheets referenced within IE conditional comments mark-up and the CSS is applied.

Luckily there are some workarounds which we were able to use. In my case I was able to set the EnablePageHeadUpdate property to false so the head content was not updated for each Ajax callback.