Indeed, the MSDN documentation is correct and this is the expected behavior.
The items that are not visible have not been created yet and are not part of the visual tree. When you switch to a tab item, its content is only then fully initialized and added to the visual tree. Respectively, it is removed form the visual tree when not visible. Unfortunately there is no unloaded event that can be handled.
This is not to say that its template is applied multiple times, the template is applied just once. (Unless it is changed).
If this does not work in your scenario, maybe I can give more advice if I know why you need the preloading of the objects or them staying in the visual tree.
the Telerik team