Thank you for your interest in the RadToolBar for Silverlight.
As we are aware of some issues with our controls inside the MS Blend we will highly appreciate if you send us more information: screenshots; sample projects; steps to reproduce.
About the tool bar. Is it possible to share with us what kind of a content you are trying to initialize with. Actually the tool bar is an items control, but we never limited its items to a certain type - you can try with different button types, text box, combo box even expander.
the Telerik team