I'm experiencing problems whilst dynamically loading user controls into a multipage with a tabstrip. I've looked at your example (http://demos.telerik.com/aspnet-ajax/tabstrip/examples/applicationscenarios/loadondemand/defaultcs.aspx
) and am doing something similar, however, I have noted that you are experiencing the exact same problem in the demo.
If you remove the RadAjaxManager, you'll notice that everything works as intended ie the right user control is displayed in the ViewSource. The problem is, you get the nasty postback!
I have tried various things to try rectify the problem without any success.