Thank you for writing.
The observed behavior is the default behavior of RadDropDownList and currently it cannot be changed. If you share with us the exact scenario that you are after, we will be happy to help you achieve is by using RadDropDownList.
We do not offer any guidance on transferring the standard controls to RadControls. There are numerous cases with every control and covering them in a guide book is not an easy task. We are trying to keep our controls behavior and API as close as we can to the standard controls in order to make is easier for the users to accommodate RadControls in their applications. However this cannot be achieved in all scenarios. If you have any difficulties achieving some scenario, feel free to contact us and we will help you with it.
I hope that then provided information addresses your question.
the Telerik team