How do you assign the report to the report viewer? If you are using a web app/site, please set the EnableViewState property of the viewer to false as there is a slight issue we introduced in Q1, which would be addressed for the upcoming service pack. If this is not the case, please open a support ticket and attach a sample project that shows the abnormal behavior. Once we review it, we would be able to provide you with more info.
All the best,
the Telerik team
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