When you give the TabControl a ContentTemplate and bind it to some collection of items, then switching between tabs makes the TabControl unload the content of the last active item and load the content of the newly selected item. The reason is that the RadTabControl has only one ContentPresenter which holds the currently selected RadTabItem for performance optimization. And since the load/unload operations involve add/remove actions in the visual tree, the content does not keep its state.
However, we have logged this issue as a feature request in our PITS where you will be able to track its progress and vote for it thus increasing its priority.
As a workaround, you can keep the state of the RadTabItem's content in a ViewModel. If you can elaborate on your scenario and the ViewModels we will try to provide you with a possible implementation.
the Telerik team
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