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.

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.

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.

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

SelectedItem does not respect the Reset collection changed action.

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.

When a TabItem has a width (and the TabControl - don't) and if you try to resize the window so that the width of the window is less than the width of the TabItem - the TabItems start jumping

When a RadDocking is located inside a RadTabControl and the RadPaneGroup contains only one RadPane the content is scrolled(if located inside a ScrollViewer)

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);
}

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

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

ICommandSource implementation for RadTabControl. It might be implemented either as CLR and dependency properties, or as attached behavior.

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.

Basically I want to see only full tabs, not part of a tab.  Those tabs that aren't visible should be displayed in the dropdown only, the tabs that are visible should not be displayed in the dropdown, and the tab control should resize (to a shorter width) to only show tabs that are visible

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

ItemsSource does not support CompositeCollection