Drag and drop from Visual Studio Toolbox to the designer area doesn't allow you to drop the corresponding control inside the content of the selected tab item. 

To work this around, add a Grid panel with transparent background inside the RadTabItem's in XAML. You can do this also  through the toolbox.

 <telerik:RadTabItem x:Name="RadTabItem1" Header="Tab item 1">
	<Grid Background="Transparent" />
 </telerik:RadTabItem>

When you select the RadTabItems via Keyboard or Mouse, Narrator or other Accessibility tools like NVDA do no read the selected tab.

This is a bug in the RadTabControlAutomaitonPeer / RadTabItemAutomationPeer's code.

Usually screen readers read "Selected Tab One", "Selected Tab 2". This is how MS TabControl is read actually.

TabControl's TabItems aren't properly updated on attempt to change the theme palette variation runtime until any of the items is selected. Check the following video - https://www.screencast.com/t/jMj0EZqFfy.

There are several possible workarounds which include:

• Clearing all merged resource dictionaries and re-merging them
• Increasing and decreasing the height of the MainWindow by 1 after loading the chosen palette to force the refresh
  

When pressing the Alt key, the access key of a given element must be displayed. Inside the Header of a TabItem it is not. The issue is not reproducible with the standard MS TabItem. It seems that it is related to the Foreground binding of the control. There is a workaround as shown below.

<telerik:RadTabControl>
    <telerik:RadTabItem >
        <telerik:RadTabItem.Header>
            
                <AccessText Text="_Tab 1"
                            Foreground="{Binding RelativeSource={RelativeSource AncestorType=telerik:RadTabItem},
                            Path=Foreground}"/>
        </telerik:RadTabItem.Header>
    </telerik:RadTabItem>
</telerik:RadTabControl>

When you have the TabStripPlacement property set to something other than Top and you try to hide the TabControl border by setting the BorderThickness property to 0. The border is still shown. If you have TabStripPlacement set to Top the border disappears.

As a workaround set the BorderBrush property of the RadTabControl to "Transparent".

Scrolling in TabStrip does not work well when TabStripPlacement=Left or Bottom and  ScrollMode=Item. Pressing the Scroll Buttons scrolls the entire set of tabs.

The TabItem doesn't changes when selected Item in the VS2010 designer.

UPDATE:
The issue is present also in the VS2008 and Blend.

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