Different behavior of example in xelatex vs. pdflatex

[samcarter]

Consider this example from the beamer user guide "9.3 Commands with Overlay Specifications" (also shown in https://tex.stackexchange.com/q/494246/36296)

% !TeX TS-program = xelatex

\documentclass{beamer}
\setbeamercovered{transparent}
\begin{document}
\begin{frame}
Shown on first slide.
\onslide<2-3>
Shown on second and third slide.
\begin{itemize}
\item
Still shown on the second and third slide.
\onslide+<4->
\item
Shown from slide 4 on.
\end{itemize}
Shown from slide 4 on.
\onslide
Shown on all slides.
\end{frame}

\end{document}

On the first slide "Shown on all slides." is visible with pdflatex/lualatex, but dimmed with xelatex