There is two possible solution till we provide a better API - you may mark as handled the routed PreviewDrag, Rotate events for a shapes that you want to be readonly. Or better you may handle the SelectionChanged event and regarding on the selected shape - you may change the IsRoation/Resizing Enabled on the diagram. This is a problem that we'll address as soon as possible - possible for the Q2.Sp1. You can also track the issue progress here.
the Telerik team
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