Thank you for the additional details, dave, much appreciated. I was able to confirm this issue.
I can suggest you to add the content items to the RadPanelBarGroupElements when the RadPanelBar is in the ListBar style. Then subscribe to the Load
event of your application's form and change the style of your RadPanelBar to the outlook nav pane style.
I'm deeply sorry for the inconvenience. We will research and fix this behavior as soon as possible.
If I could be of your further assistance, please write back.
All the best,
the Telerik team