didn't know I have to return. so the next time, the card was still in my passport when i tried to cross the border. so i was really given a hard time. and then the 2nd time, i returned the card to Canadian customs and thought this time it should be ok. but to my madness, the 3rd time when i went to buffola (at that time, i was even holding my Canadian Passport) and they gave me a hard time again saying they didn't receive the returned card from Canadian Customs.... My belief is, they will challenge you whatsoever as long as you had broken their rule once.....