Do you mean you get empty list in case of AJAX Manager added in a MasterPage scenario? We are aware of a similar problem related to the VS 2008 design-mode. You can find more info in this blog post. If so, I'm happy to inform you Microsoft has already fixed the issue with the VS 2008 SP1 Beta so you can download and install that to resolve the problem.
All the best,
Konstantin Petkov
the Telerik team
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