That is astoundingly confusing and pretty out of character from how he was established in season 4. :/ 

The only theory I can propose to explain it is that although he’s incredibly intelligent, the thought of Mike being evil or going out of his way to harm people (be it as himself or through one of his alters) is too much for the bubble boy, and he put up a mental block in his subconscious. This is a phenomena in real life, do it’s not too outlandish to propose this. After all, Cameron had NO friends before he met Mike and Zoey. To think that Mike is evil or has an evil personality would be a truth Cameron would not want to accept. He was readily able to help Mike with his personalities in s4, but none of them had bad intentions (even Vito was just a butt, not so much evil or terribly mean).