Handling different client and server content - not showing initial render

In the hydrateRoot page, it is mentioned that
"This way the initial render pass will render the same content as the server, avoiding mismatches, but an additional pass will happen synchronously right after hydration."

which means that the initial render on the playground should show "Is Server", but it shows directly "Is Client" which is very confusing for learners and doesn't show the real behavior.
I tired opening the sandbox in external window, and it indeed shows "Is Server" first and then changing to "Is Client" as expected.

In the Website:

In The sandbox (using the fork button):

Commencez par le playground intégré à la page hydrateRoot et comparez son comportement avec celui du sandbox externe ouvert via le bouton fork. Reproduisez l’exemple et suivez la manière dont le playground gère l’hydratation et son rendu initial. C’est terminé lorsque l’exemple intégré affiche brièvement "Is Server" avant de passer à "Is Client", conformément au comportement documenté.