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

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

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

The selected item could have a different header template so that it will be differentiated from the rest of the  tabs.

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

Display in overflow menu only the items that are not visible in the tab strip.

When you have implicit DataTemplates applied to items the binding expression is lost on selection changed.

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.

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 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.

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.

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

RadTabControl is currently designed to support scrolling of RadTabItems only when any of them is currently focused. An ability to scroll RadTabItems without explicitly focusing them should be provided.

When the window of an application that has a TabControl with Left/Right TabStripPlacement is resized, the measure of the TabStrip is incorrect and the ScrollButtons are in Disabled state. All Tabs should be visible when the window is in its normal state and should be scrollable.

TabControl: The tab items and their content are not disposed correctly due to the RadTabItemAutoamtionPeer.

Introduce "Add new tab" button as in the RadTabbedWindow control which creates a new tab upon click.

This happens if you use the DropDownOpened event of RadTabControl in order to reorder the DropDownItemsSource of the event arguments. In this case, the synchronization of the selection between the drop down and the tab items is broken.

To work this around, you can disable the default overflow button and implement a custom one in the AdditionalContent of RadTabControl. Check the attached project for a sample implementation.

Currently, when scrolling tabs in a TabControl using the mouse wheel, the direction of the scroll is the opposite as tab controls of many other applications, for example all web browsers scroll tabs in the opposite direction as the Telerik RadTabControl.

This behaviour may cause frustration in the end user and damages the user experience. I think it's necessary to expose a way to allow inverting the RadTabControl mouse wheel scroll direction.

The scroll buttons are visible when the visible area is enough to display all tabs and the TabStripPlacement is set to Left/Right.