Prism View is incorrectly initialized when associated with a region We have created a SDK sample with a CustomRegionAdapter for the RadTabControl and its implementation can be found in out SDK repository(https://github.com/telerik/xaml-sdk/tree/master/TabControl/PRISM/CustomTabControlRegionAdapter)
We have created a SDK sample with a CustomRegionAdapter for the RadTabControl in which the ActivateView logic is implemented. You can find the example in out SDK repository(https://github.com/telerik/xaml-sdk/tree/master/TabControl/PRISM/CustomTabControlRegionAdapter)
The TabItem doesn't changes when selected Item in the VS2010 designer. UPDATE: The issue is present also in the VS2008 and Blend.