This issue has been logged in our system for improvement. While we are fixing it, you can set drilldown actions to another type of report item, so it can work properly in Preview.
We are sorry for the inconvenience.
In case you are not using a Panel item for the drilldown action, and you are still experiencing this issue with other report items, it would be best if you open a support ticket, where you can zip and attach a sample report definition exhibiting the described issue. Once we review it, we would be able to provide you with more information.
New HTML5/JS REPORT VIEWER with MOBILE AND TOUCH SUPPORT available in Telerik Reporting Q3 2013! Get the new Reporting version from your account or download a trial.