Thank you for the clarification. The problem is coming from the fact that the MS AJAX framework does not update the head element of the page where our control would normally register its styles. So when you try to show it on ajax request, it would not pick up the styles. The workaround is to either hardcode the .css files in the head element or place another instance on the page with display:none. The good news is that we are working on a workaround for this MS AJAX limitation which will be available for the Q1 release.
Sorry for the inconvenience.
the Telerik team