Not the highest priority bug in the world, but I ran this:
% arc land Landing current branch 'profile-model-test'. TARGET Landing onto "web-perf", selected by the --onto flag. REMOTE Using remote "origin", selected by following tracking branches upstream to the closest remote.
It said: "selected by the --onto flag", but I did not actually use the --onto flag. (In reality, it landed onto web-perf because that was the upstream; profile-model-test was a tracking branch.)