I tested your code against the latest RadForm version and I was unable to reproduce the problem.
What we've changed regarding RadForm in Q2 is its designer. Now it resembles more the Document Designer of Windows.Forms.Form class. Does your code execute in context of VS designer? Does you form inherit from another RadForm?
Otherwise I am not able to determine any other possible reason for this issue. RadForm relies on base (Form) Controls collection which does not contain any code related to the problem you are describing.
I hope this information can help you determine what is causing this problem.
If the problem persists please send us the complete source code of the form, along with description how you are using it and when the problem occurs.
All the best,
the Telerik team