Excuse me for the misunderstanding.
As to design error - it is expected in this case because there is no data which can be calculated and shown. The data will be loaded once you start the application.
However, you said that this problem starts showing after upgrading to Q2 2012 SP1 version. Could you point the version when this exception doesn't occur? We will try to find why there is difference between the two versions. Thank you advance.
All the best,
the Telerik team