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".

If you define two UserControls in a project and you add two RadTabControls - one RadTabControl per UserControl, then in design-time you can only change the selection of one of the tab components.

When the RadTabControl AllowDragReorder property is set to True and the control contains multiple rows with tabs, the dragging operation cannot be properly executed and completed.

SelectedItem does not respect the Reset collection changed action.

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

Exceptions are occuring on ALL bindings, not just with RelativeSource

Command="{Binding AddCommand}"

will also raise an exception.

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

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.

Improve the design-time support of the TabControl. For example add an option to add new RadTabItems in the control.

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.

Click event of a Button in the HeaderTemplate is not fired properly when another button outside the tab has IsDefault property set to true

The animation when moving tab is mandatory for a proper user experience.

Using Xaml declared tab control with identical tab item headers will result in selecting the first occurance of selected text from the drop down content.
Add support for distinguishing different items in the drop down content (use DropDownDisplayMode=Visible) during selection and match to the corresponding TabItem.

In the VS2010 designer the selected tab is the last one even if the SelectedIndex proeprty of the TabControl is set to 0. The issue can be reprodiced in a scenario where the RadTabControl is defined in a RadWindow control.

Change the TabItems layout when the TabControl OverflowMode="Wrap" with TabStripPlacement="Bottom" :
1. Let's say the wrap results in 3 lines. What we would expect is line 1 and 2 to be filling the entire width and line 3 to be partially filled. What we experience is line 1 partially filled and lines 2 and 3 filling the entire width 
2. When clicking on an item the lines swap around. The partially filled line can end up on top, in the middle or on the bottom. Clicking on items that cause tab rows to move up should re-flow the wrap.
3. Ideally - to look good - the logic should stretch the 'complete' rows to the entire width - i.e. it should adjust tab sizes to fill the entire width available on 'full' rows.

When the SelectedIndex property is read during animation the CLR wrapper will throw InvalidCastException because of invalid cast to int. The object returned from GetValue is DeferredReference object.

Preserve the content of tabs during tab reorder

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

Create custom region adapter for the RadTabControl

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)

Fire the PreviewSelectionChanged event before user-initiated selection