What you observed is the expected behavior of the control. The PanelBar is a hierarchical control and each of its items has a header and a collection of subitems - thus, you shouldn't expect an item to have a content other than what is displayed in its header. If your data is not hierarchical, probably our OutlookBar or Expander controls will be better suited to your scenario. Please take a look at the links below and let me know if any of these controls will fit your needs.
If you insist on using the PanelBar for displaying non intrinsically hierarchical data, this is still possible but would require some re-templating of the control, since this is not specifically the type of scenario it is intended for.
All the best,
the Telerik team
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