Blend does surprise me from time to time.
All the controls that are visible on the Blend surface are actually "live", i.e. all their internal logic is preserved, you can even debug them while they are running there.
When you set the IsSelected = true of a TabItem, the TabControl makes sure that no other item is selected (sets the other properties to false). It seems that when the property is changed by the TabControl Blend does not notice and the Xaml of the TabItem is not changed accordingly - the control is in a state that is not matched by the xaml. When I test it the control runs according to the xaml, i.e. the last item to have IsSelected = true is selected, if no such item exists, the Selected index is used (default value = 0, if at least one item exists)
I will investigate the disparity though I am not sure that we have control over how Blend generates the Xaml.
This behavior might be a little frustrating if you have to switch the content often. One workaround would be to use the SelectedIndex property of the TabControl instead of switching the IsSelected properties.
Thanks for the feedback! I will check whether Blend behaves similarly in other cases as well. And of course, if this turns out to be a bug in the control, you'll get your points.
All the best,
the Telerik team
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