Most times I am trying to do something in design-time which should only be executed at run-time within a custom control and need to test on the DEsignMode property of the control.
There's a good chance that it might be the same problem.
Here is the link to the newest Extensibility DLL that might resolve the problem. No promises, but, it might work
http://forum.strataframe.net/FindPost9739.aspx