For every Sunbelt refugee who has tried to leave high tax bills behind in the cold Northeast, Julian Robertson scored a victory this week. By proving that he was outside New York City for half the days in the year 2000, the former hedge-fund titan avoided $27 million in city taxes, thanks to a ruling by New York's tax court.

No thanks are due the New York State Department of Taxation and Finance, which had ruled he was a resident and therefore liable for the multimillion-dollar tab. In the upside-down world of tax law, where...