I see I tought since when I first arrived in Canada they asked me if I have lived in the USA, I said no and they let me in even tho I lived in the USA for 5 years before, also while in Canada I knew many accepted refugees who committed serious criminal acts in the USA or other countries and they never did a background check on them, which really pissed me off to be honest, but maybe is different for when someone gets rejected.
To answer live&love: Is not so rare as you think, the deportation center where I was being held was packed with people ready to be deported, is just that this doesn't hit the news, the police in Montreal (where I was living) is actively working together with immigration, not so in Toronto (from the own words of the police officer).
In my case I went to talk to a neighbor who didn't let his surrounding neighbors (including me of course) sleep during the night, he responded in an aggressive way, I put my arms in his shoulders to calm him down, big mistake from my part and the rest is history, others in the deportation center had committed a traffic violation, had a fight with someone, etc... but don't think is so unusual, is happening.