1. Go to https://www.telerik.com/kendo-angular-ui/components/editor#angular-editor-example
2. In the Angular Editor Example. click in the editor and type one letter to enable the "Undo" toolbar button
3. Navigate to toolbar via Shift+Tab key
4. Use the left or right arrow key to navigate to "Undo" button 
5. Use Enter to trigger the "Undo" button which should then re-focus the editor and disable the "Undo" button
6. Immediately press Shift+Tab key to navigate back to the toolbar with the "Undo" button disabled

Expected behaviour: The disabled "Undo" button is focused so that toolbar navigation with left or right arrow keys is enabled.
Experienced behaviour: The toolbar is permanently unfocusable with keyboard navigation and the element (theme selector) before the toolbar is focused. It is no longer possible to navigate to any buttons in the toolbar with Tab or Shift+Tab at this point. This happens with any toolbar button that becomes disabled after triggering such as the "outdent" button.

NOTE: The expected behaviour actually works in the jQuery Editor (https://demos.telerik.com/kendo-ui/editor/all-tools), so the Angular Editor should be fixed to match.