Hello Kirk Quinbar,
I prepared a sample for you that demonstrates a possible approach. Basically, I play with the IsEnabled property of the RadPanelBarItem and don`t use PreviewExpanded and PreviewCollapsed events in order to avoid cycles, propagating of invocations and etc. Please examine the solution and let me know if it fits in your scenario. It should be easy to modify it , so please let me know if you need further assistance.
the Telerik team
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