Workaround:
Use the PreviewMouseLeftButtonUp and PreviewMouseLeftButtonDown events of the DropDownMenuItem. Handle the first event and invoke DropDownMenuItem.MouseLeftButtonUpEvent in the second in order to workaround the MouseLeftButtonUp event fired from the DropDownMenuButton and to call the logic for selecting the tabitem only when the dropdown menuitem is clicked (not just hovered). 

<Style TargetType="telerikTabControl:DropDownMenuItem">		
        <EventSetter Event="PreviewMouseLeftButtonUp" Handler="DropDownMenuItem_PreviewMouseLeftButtonUp" />
        <EventSetter Event="PreviewMouseLeftButtonDown" Handler="DropDownMenuItem_PreviewMouseLeftButtonDown" />
</Style>

private void DropDownMenuItem_PreviewMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{		
		e.Handled = true;
}

private void DropDownMenuItem_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
	var item = (sender as DropDownMenuItem);
	MouseButtonEventArgs mouseEventArgs = new MouseButtonEventArgs(Mouse.PrimaryDevice, 0, MouseButton.Left);
	mouseEventArgs.RoutedEvent = DropDownMenuItem.MouseLeftButtonUpEvent;
	item.RaiseEvent(mouseEventArgs);
}

The CommonStates of the control aren't applied and this is why you can't add any storyboards for the normal and disabled state of the control.

Can't apply transitions when changing the visual state of the RadTabControl or its items

Add a visual state for the selected tab item representation in the DropDown menu of the TabControl.

The TabControl ScrollMode property doesn't work as expected when set to "Item"

When navigating with tab key (without setting tabindex) first highlights the RadTabItem then its content. Setting a tabindex on a control in the tabItem`s content works the opposite way

Using  ArcGIS API for Silverlight/WPF version 2.1 in the TabControl throws exception in design-time

Tabcontrol doesn't work correctly when we set the properties TabOrientation="Vertical" and AllTabsEqualHeight="False". The Header are always Aligned left no matter the value align property.

DECLINED: This issue cannot be reproduced with R3 2016 release version.

DECLINED: This issue is not reproducible with R2 SP1 2016 Release.

Loaded event of the RadTabItem's content is fired twice in WPF.

Declined: The behaviour is caused due to the way how the WPF framework operates with ContentControl and their Content property(the RadTabItem is HeaderedContentControl which derives from ContentControl). The Content property is automatically registered to the LogicalTree when it is set, this is causing the first loaded event to be fired. After a selection is made the RadTabControl inserts/visualizes the Content of its selected RadTabItem in its ContentPresenter, this causes the control to fire its loaded event as it is loaded into the VisualTree.

private void Content_Loaded(object sender, RoutedEventArgs e)
{
	if (VisualTreeHelper.GetParent(sender as DependencyObject) != null)
	{
		// Execute the logic for LoadedEvent.
	}
}

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)

Fixed in LIB version: 2014.3.1103

Pressing "Tab" key does not change the focus when there are several controls in a TabItem.