Workaround: Set HorizontalScrollBarVisibility property to Visible in order to show the scrollbar: 
<telerik:RadTabControl ScrollViewer.HorizontalScrollBarVisibility="Visible" .../>

or use Loaded event of TabControl and change the Height in order to trigger SizeChanged:
private void xTab_Loaded(object sender, RoutedEventArgs e)
{
    this.Height++;
    this.Height--;
}

In version 2016.2.613.45 of the Office2013 Theme, there is a problem in the control template for the RadTabControl. The ContentBorder element properly gets it's BorderThickness from the TemplatedParent, but the PlacementStates VisualStates override it with hard-coded Thickness (0,1,1,1 in the case of the "Left" Visual State) in their storyboards rather than doing an appropriate transform of the Thickness. This makes it impossible to override the BorderThickness for the control in any state other than the default layout without copying and replacing the entire control template. This appears to be a change in behavior since the (Februray 2016?) release, but I cannot be sure as the old theme files were uninstalled during the upgrade and the telerik.windows.controls.navigation.baml file is not properly decompiled in JustDecompile.

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

A System.Windows.Documents.Hyperlink' is not a Visual or Visual3D Exception is thrown when you click on a Hyperlink inside a RadTabControl and then try to scroll using the MouseWheel


Available in LIB version: 2014.3.1409

The Align property is not respected in the following themes: Windows8Touch, Office2019

In R2 2019 there is a regression bug in RadTabControl.

A design time error occurs when referencing NoXaml assemblies. 

error appears when the control is placed inside a RadTabItem

Scheduled for:
The fix for this issue will be available with LIB (version 2019.1.204) scheduled for publishing on Monday, 4th February 2019.

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 there are tabs present which have their Visibility property set to Collapsed and the ScrollMode of the control is Item, scrolling the items via the arrow buttons skips items unexpectedly.