Yep....check the Airline. Canada has a law that if anyone is found inadmissible to Canada, the Airline that bought them, must also take them back....at no charge.
So some Airlines can be very strict about whom is allowed to board. My son, who is a PR, is currently in the UK staying with my parents for a few months. He booked one way to the UK. He has now booked a one way flight back to Canada for January 2011, the booking agent for Air Canada insisted on a copy of his PR card, before they would except the payment for the one way ticket back to Canada.
I believe this has nothing to do with Canada, nor the immigration officers but more to do with the Airline.