To optimize the performance RadOutlookBar uses a single ContentPresenter which holds only the Content of the currently selected RadOutlookBarItem. Each time the selection is changed the content of the last selected item is unloaded from the visual tree and the content of the newly selected item is loaded. Because of this the current state of the selected item's Content is lost.
To preserve the state you can set the IsContentPreserved property to True.
Example 1: Enable content preserving in XAML
<telerik:RadOutlookBar IsContentPreserved="True" />
Example 2: Enable content preserving in code
this.outlookBar.IsContentPreserved = true;