In an unexpected twist in the Microsoft legal saga, a federal appeals court on Monday ordered a temporary halt to the work of a court-appointed Harvard law professor who had a significant role in the antitrust case.

The decision represents a significant but temporary victory for Microsoft, which fought strongly to disqualify Lawrence Lessig as a “special master” appointed to prepare a report on technological issues in the dispute.

Microsoft last Friday argued that Lessig was biased against the company and challenged the legality of a lower court’s decision in naming the professor to the post.

“We see this as a very positive step but it’s only one step in a longer deliberative process,” Microsoft spokesman Mark Murray said.

The U.S. Circuit Court of Appeals for the District of Columbia, in a one-page order, granted Microsoft’s request for a stay, effectively freezing Lessig’s work.

It set oral arguments on the Lessig matter for April 21 - the same day Microsoft and the Justice Department were to argue an appeal on a related lower court order for Microsoft to separate its Internet Explorer software from Windows 95.