Question: how do you know gcd and Gcd different in maple?

why are the results of gcd(x^2+1,x+1) mod 2 and Gcd(x^2+1,x+1) mod 2 in maple  different ? 

I know the  `mod`(gcd(x^2+1, x+1), 2);
                               1
`mod`(Gcd(x^2+1, x+1), 2);
                             x + 1

but how do you explains this question? give me reason?

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