I tested the reported behavior and it seems that the DisplayMemberPath property of RadOutlookBar does not work in WPF and this is why the Headers of the items are not displayed. I logged an item in our feedback portal
that relates to this issue. You can track the issue's status by following the feedback item. I also updated your Telerik points as a small sign of gratitude for reporting this behavior.
As a workaround you can use an implicit style targeting RadOutlookBarItem instead of the DisplayMemberPath property. You can define the style in the xaml page (the view) where the RadOutlookBar control is defined.
Here is an example in code:
I hope this information helps.
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