The controversy surrounding the appointment of Supreme Court of Canada Justice Marc Nadon is leading to a greater possibility of tie decisions at the country's top court.

Since the fall session started Oct. 7, four of the eight cases at Canada's top court have been heard by an even number of judges.

They include the case of Mohamed Harkat, an Ottawa resident challenging the constitutionality of national security certificates, and Christopher Whaling, a B.C. man who was in prison when the federal government changed the rules on early parole.

Last month, Prime Minister Stephen Harper appointed Nadon to fill one of the three Quebec seats at the Supreme Court. Within days of Nadon's swearing-in ceremony, Toronto lawyer Rocco Galati argued Nadon does not meet the requirements to be appointed from the province of Quebec.

Nadon decided to step aside until the controversy subsided. Instead, it intensified when the Quebec government announced it would challenge the appointment based on Nadon's residency.

Since then, the federal government has introduced legislation to rewrite the Supreme Court Act, and has asked the Supreme Court of Canada for its opinion on the constitutionality of Nadon's appointment.

In the meantime, the court has instructed Nadon to stay away from the court and his new colleagues.

There are nine members of the Supreme Court and most cases are heard by all or seven judges.

Occasionally, the court sits with five. While not unheard of, "It is extremely rare to see an even number of judges sit and decide a case for the very obvious reason of trying to avoid a tie," said Adam Dodek, a University of Ottawa law professor.

As an observer of the top court, Dodek added, "There's no good explanation so it continues to be a big mystery in the legal community."

That mystery will remain unsolved.

Even number 'may prove problematic'

While it's up to Chief Justice Beverley McLachlin to decide who and how many people will hear an appeal, a spokesman for the court told CBC News that the court will not comment on the composition of its panels of judges.

Stéphane Beaulac, a University of Montreal law professor, says that in the past, panels of eight were convened as a consequence of death or illness.

He says he can't understand why the chief justice would choose to hear cases with an even number when she would be aware of the remote but possible outcome of an even split.

"There's no precedent in recent history of the Supreme Court of Canada that they would sit with an even number," says Beaulac, "In our tradition, it is odd and it may prove to be problematic."

In the event of a tie, the decision of the lower court would stand.

Dodek explains there would be a statement from judges on each side to explain their points of view, but "the authority of the statements would be limited if you had a tie, so it would just in some ways create more confusion than it would clear up."