Suspected in an IRC troubleshooting session, verified experimentally. On a fresh install from amd64 13.0-R DVD1 with ports tree: ls -ld /usr/ports/x11/gnome* # shows gnome3 with Apr 9, 2021 timestamp portsnap auto ls -ld /usr/ports/x11/gnome* # shows gnome3 with Apr 9, 2021 timestamp and gnome with Mar 24, 2022 timestamp.
Forgot to say: IMO, portsnap should balk (maybe with suggestion to rm -rf /usr/ports) if it finds a not-empty /usr/ports on first run, for POLAness. If someone rules "working as designed", then it needs to be documented, because trap for the unwary.