Non-interactive Web controls are tab stops with unthemed focus rings

Tabbing through a Web app unexpectedly lands on non-interactive controls — Separator, Label, ProgressBar, GroupBox, and the TabPanel's tab strip — and each one then shows the browser's default blue focus ring instead of the app theme's focus ring. These controls cannot be operated, so they should not join the keyboard tab order by default, and anything that can legitimately receive focus should use the theme-aware focus ring like the other Web controls.