When you have declared a RadTabView with a single item and you try adding items at runtime - the new TabViewItems are added to the Items collection of the control but the UI is not updated.

Support for interactive TabHeader content (i.e. Buttons, Checkboxes) that does not invoke the tab selection and is aligned next to the tabs

Allow different width tab headers. For example, 200, 100, 100.

Available in minor release 2018.2.727.250. It will also be available in the R3 2018 release.

This feature request asks for the option to align the TabViewItemHeaders to one side of the HeaderPosition, using the minimal amount of horizontal space (rendered as if they're in a horizontal StackLayout)

As a good example, the UI for WPF TabControl does this, notice the tab headers are left-aligned: https://docs.telerik.com/devtools/wpf/controls/radtabcontrol/overview2